Except the majority of the advertised improvements to the journey times to the West Country are not coming from omitting stops but from from the superior acceleration and braking of the units.. plus the improved dwell times (maybe 30 seconds per stop?).
Anyway I’m sure ‘railperf’ has enough data out of Reading on the 800s electric acceleration and braking curves from 70-110 and 110-70 to tell us whether it would make a difference...
I have established that the superior acceleration from rest to 125mph (in electric mode) is worth around a minute's time saving over an HST. Multiply that by the number of stops, and you gain that time saving.
Braking is slightly more contentious - as timetables are based on braking rates of approximately 5 to 6%G - mainly for safety reasons. Although _ i understand - the 800's have better brakes than HST's, I have not read anywhere that drivers are going to be retrained to brake later and harder than they do now. Undoubtedly, as drivers become more confident and understanding of their machinery, and how it performs in good and bad weather, they may be able to utilise the better braking performance when running late. But that is likely to be in isolated cases - as it is now with any train - rather than an widespread policy change. Especially if drivers have to be signed to drive both sets of traction for a period of time.
As an example , GWR's recent 'speed' run took 3 mins 40 seconds from Passing Twyford at speed to a rest in Reading. However, I have seen logs of HST's achieving that in 3 minutes flat. So HST's have pretty good brakes, but likely that braking would not be allowed by today's safety conscious - defensive driving standards to prevent SPAD's and station overruns!
And the braking has to be achieved in both dry rail - and very slippery conditions to ensure reliability of the timetable.
For example, in wet weather - GEML Class 90's suffer terrible wheelslip and have to be accelerated gently to linespeed. In wet conditions - the timetable suffers considerably and a 10 minute late arrival is not uncommon. However, in dry conditions - the 90's can obliterate the timetable easily making up time on every station to station section!