1x10 would be shaped by a number of factors including increasing off peak and weekend capacity without running more trains and avoiding expensive double crewing.
There is a clear inconsistency between how you and Clarence Yard see the world, even down the class of train and whether the journey time will be compared with an express or not. You have spent a long time arguing the peak busting 387s and IETs will fix Reading only to be told quite clearly that they won't and Reading punters will have to use the 345s which will take 50mins to Paddington. I maintain that as today they won't use them unless you are going to make them and the message about more seats will ring hollow.
There are also a lot of big risks emerging in this brave new world, more trains rammed through an already congested and unpunctual bit of railway. Granted having the 345s disappear down the tunnel will help, but there is a lot on the debit side and having half the off peak arrivals needing to pair up for the peak is another problem that wouldn't exist if they hadn't gone for coupled units.
I have yet to see evidence of this peak crowding from west of Didcot heading towards London and having read the Great Western RUS there wasn't any back then anyway.
If the new service does involve not stopping a good number of trains at Reading, the risk is carrying empty seats all the way to London rather than fixing a problem that may not even exist.
I did not say IETs and 387s alone would 'fix' Reading - if you had bothered to read my earlier posts, you would see plain as day that I argued that some passengers may opt to use Crossrail services instead - in just the same way that some passengers from Reading use SWR to Waterloo now. But you refuse to accept that anyone may even contemplate changing their travel habits, never mind actually do so.
The only way to 'fix' Reading to your satisfaction would be IETs shuttling up and down between the two points, without pesky passengers from anywhere else, locally or further afield, getting in the way
And even though you are obsessed with Reading, if passengers in other places in the Thames Valley opt to switch to Crossrail, then that can also free capacity on other services for the oh-so-important Reading commuters. I repeat, for the umpteenth time now, it is not all about Reading peak passengers - never was, never will be.
Again, do some research - the only trains that will not be stopping at the centre of the universe are perhaps the odd peak Didcot starter that then calls at Twyford and Maidenhead to shift the crowds there and the two off-peak IET services to and from Bristol, operated by five-car sets, plus the third peak service per hour to/from Bristol and South Wales. Though no doubt some Reading commuters will still get on board the latter anyway and then throw a strop on Twitter because they ended up at Chippenham or Bristol Parkway with an excess fare to pay.
This is purely hypothetical of course:
Everything that maps to the current high speed long distance services which would be 2xWales/Bristol, 1xeach Cotswold, 1x West of England. For three peak hours approx 1630-1930 that is 21x10car for a start. Until electrification the 1x Oxford will also be required but some will come back within 3hr.
Bedwyn is a real headache. At the moment using HSTs seems to generate lots of very quiet trains to Frome, Westbury and Paignton because there is nowhere to turn round between Newbury and Westbury and the Bedwyn service doesn't or didn't serve London in the peak. The current plans don't fix this problem unless the plan is to start splitting 2x5 at Newbury. I would suggest at least a 8 car siding and an IPEMU/FLEX solution to the lack of wires with a limited semi fast service 1x7 off peak 1x10 peak serving the larger places like Newbury, Pewsey and Caste Cary.
Then you need a hard nosed approach to the extremities. There is already a lot of dead wood that once it gets crystallised in the timetable proves very difficult to uproot. Set a revenue per hour/mile and or a passenger number threshold and if both legs fail the test it either becomes a DMU/EMU or a connecting train. This would probably mean a lot of off peak miles to places like Paignton, Hereford and Cheltenham disappear from the current plan.
Everything that is left and doesn't touch either London peak could be formed by a 1x7 formation that is not divisible or expandable and would seat roughly the same as a current low density HST.
Next is the new express trains which off peak I believe serve the two Bristol stations at 2tph off peak and then split in the peaks to run fast Chippenham and Bristol Parkway to Wales. I suspect they get nowhere near filling 7 off peak nor 10 cars in the peak unless more stops are added.
Though they would probably pass a test above, they look and feel like HS2 purely abstractive showboating that loses the government money in exchange for purely illusory and intangible value of time saved.
There is a strong case not to run them at all, even on the peaks, on the grounds that the already poor levels of punctuality prove there is no space for them. Alternatively they could run 1x7 in the peak only.
On lease costs you already have a very large fleet of 2x5 so in vehicle numbers there would not be a great variance to the present and far fewer train miles being operated by this fleet. The current cars per train across both fleets is 9.45 slightly more than having 80% 1x10 and 20% 1x7. On the current fleet size of 605 vehicles that would equate to 12x7 and 52x10 although you probably don't need more than about 35-40x10 to cover both peaks depending on what the Venn diagram looks like AM to PM
Yet again, do some basic research - like look at a current timetable or two.
Your hypothesis falls at the first hurdle.
The Cotswold Line service is effectively two trains per hour in the direction of the main peak flows morning and evening - and has been for years - plus there is the odd Oxford-only peak run, so the 'Oxford' sets - actually Oxford and all sorts of other places, thanks to diagrams that are a bit more involved than just shuttling up and down all day - will still be required.
Nor is the West of England service one train per hour in the peaks - it is half-hourly from Paddington between 16.03 and 19.03 to Exeter or beyond.
Never mind that extra IETs were acquired in order to have enough in the fleet to cover the Oxford services. And with part of the 387 fleet now going to Heathrow Express, there probably wouldn't be enough to take over Oxford fasts even when wires do get there.
And then we get to the real giveaway, talk of 'dead wood', etc.
For all the pretend interest in life beyond Reading/Didcot we can see plain as day that all you care about is the peak service between Reading and Paddington. Far from there being a boost in off-peak capacity thanks to your 1x10 jumbo trains, there would be, er, no capacity whatever in lots of places.
Everything else and the people everywhere else who use GWR's services are clearly neither here nor there as far as you are concerned.
Your concern for the Government's money is very touching, but as Clarence Yard pointed out, it was the DfT that wanted improved service frequencies for the 'dead wood' zone.
52 x 10 coach 80x
12 x 7 coach 80x
Vs the fleet that they are replacing
52 HST's
14 x 180's
This is not what is being replaced.
When FGW last had all 14 180s on its books in 2008, it did not have 52 HSTs in the fleet. More HSTs were acquired in 2007-8 to replace some of them. The IETs are also replacing a number of Turbo diagrams on Oxford/Cotswold Line and Bedwyn services.
