As far as any% goes I don't see why you can't choose any speed you want and change it mid game too if you are using RTA. I know that the game is barely controllable on max speed (at least for me) but it useful to speed up some sections of escort missions and what not.
If you do a run you basically become the pioneer of the category. You could do a set speed category if you want and that could be added in to the rules but I don't think that is a true any% IMO.
If you have any other thoughts you can check out the IGT/game-speed dicussions over in the Age of Empires 2 (AoE) boards on this site because they have had a similar dicussion before.
As far as my opinnion I think you should be able to change game speed mid game if you can handle it and I would be opposed to 'set speed' runs
I think the max speed for Tiberian Dawn is an uncapped framerate, which gives benefit to computers with better CPUs. In my opinion the max speed should be 'Faster' like how Tiberian Sun is.
Of course, this won't matter until there are runners for this game.
