The class 92 performance concern is nonsense.
Let's look at some specs:
Class 90:
Maximum speed - 110 mph (180 km/h)
Power output - 5,000 hp (3,730 kW)
Tractive effort - 58,000 lbf (258 kN)
Class 92:
Maximum speed - 87 mph (140 km/h)
Power output (25 kV) - 6,760 hp (5,040 kW)
Tractive effort - 81,000 lbf (360 kN), 90,000 lbf (400 kN) in 'boost' mode
On key indicators such as power and tractive effort, the 92 beats the 90 hands down. With a heavy loco-hauled set (up to 16 cars I understand) the 92 will do much better up the steep gradients at the northern extremities of the WCML and should be able to accelerate the train up to maximum speed much more quickly after both scheduled and unexpected stops en-route. On a southbound it's true that a 92 may not be able to use higher speed to catch up on late running, but it can be argued that the sheer grunt available on the northern section will have made such late running much less likely in the first place.
The 73s in their rebuilt form are a slightly different case. To all intents and purposes they are new locomotives, albeit within an old shell, and with only bogies and traction motors being the major components retained (refurbished to an as new condition), whilst the engine, generator, traction control and cab equipment are all new to modern standards with all the latest safety systems and bells and whistles as provided for new traction. The new engines fitted will almost perfectly match their maximum electrical output of 1,600 hp (1,193 kW) and if, as likely, they are heavier, they should be able to exceed their historic maximum electric tractive effort of around 40,000 lbf (177.9 kN) on diesel. That is very close to a cl.37 performance in a lighter weight package, and very suitable on their own for the half trains or double headed for the whole 16 cars. By contrast, the 67 is rubbish at the lower speeds. Despite an installed diesel power output of 3,200 bhp (2,386 kW), around 2,500 hp (1,864 kW) at rail, it only develops a tractive effort of 32,000 lbf (144 kN) maximum, or 20,700 lbf (92kN) @75kmh continuously. Clearly a cl.68 is much better than that with installed diesel power of 3,800 hp (2,800 kW) and tractive effort of 71,000 lbf (317 kN), but they are limited to 99MPH. The bigger risk of the cl.73 rebuilds is, in fact, their newness. With most important components being in fact 20 years younger than those in the cl.92s, they haven't all yet been tested exhaustively in service together as a system.
Whilst I respect drivers and their experience, they and their union leadership are not engineers, planners or safety professionals. Maximum speed capability is only one aspect of performance, with available tractive effort often being more important for applications where hill climbing and good acceleration are required. With the cl.73s being effectively new locomotives there remains a risk of minor flaws being uncovered, but these should be able to be fixed in the testing process underway currently before introduction in service.
Lastly if it is British jobs the union is worried about, the 73 rebuild has provided many thousands of hours of employment for British engineers and craftsmen in Loughborough. A new locomotive would have been built overseas like the 67s and 68s.
(NB - All locomotive power and tractive effort figures quoted above obtained from Wikipedia, so usual caution applies as to their veracity)
