Agree with others this is pretty much academic because CR2 is now on the very furthest back burner.
I think though that it’s an oversimplification to assume CR2 taking over some branches would automatically allow the displaced stock to be surplus, because the idea was firstly that some other branches would retain their SWR services alongside CR2, and secondly that many longer distance routes would have frequency increases, with the current outer suburban services that switch to the main fasts between Woking and Surbiton, (about 6 or 7 in the peak hours), staying on the main suburban lines all the way into Waterloo. Then all those intended Waterloo main fast services with increased frequencies would also need extra rolling stock, and I think it would have been achieved by cascading more 701s onto slightly longer outer suburban services, releasing 450s. For example 5 car 701s could easily be used on the Guildford/Farnham/Ascot short workings, or even on Portsmouth - Southampton stoppers.