I don’t get this argument about speed. Both IET / class 80X and HST / class 43 are limited to the maximum line speed of 125MPH (where this applies).
When running on OHL, clearly the IET / class 80X has better acceleration than the HST / class 43. But then, the design of the 80X is forty years younger, so I would expect improvements in technology to have made some differences.
If either of the above trains are running a long distance, limited stop service, the extra acceleration is not going to make a significant difference anyway.
However, yes, there are most definitely areas where the design of the IET / class 80X is not as good as it should have been. And the interior fit out including the seats, layout, lighting etc. are all down to the specification, and we know where that came from…