The top speed in HD is as far as I recall the same as Pulse, those stats were not altered, possibly the top end came in by 3-5kph, but no more and it might have gone up 3-5kph I cant recall it was a year ago
The sensation though, is a little different, mainly due to the screen size and what you can see also due to what you are used to
We can make it go faster, Zone mode shows that, however in zone mode we change the ship a lot so that at super fast speeds it doesnt fly off a jump and never come down.
To have a faster class in HD would take a lot of consideration, we would need to consider the effect on each track, in terms of collision, where you can fly to, what you can see, where you get reset, etc. In short it would be a large chunk of work to add to the list of things we'd like to do. It was never planned for HD, whether we go back and look at it again, I dont know much depends on the success of HD as to what happens next.