I don't really know the difference between the versions. voodo2x.exe and carmav.exe are the ones I've seen work with Glidos. And if I remember rightly, carmav.exe checks for the CD being present, whereas voodoo2c.exe doesn't
There shouldn't be any as far as functionality and performance is concerned. voodo2x.exe is essentially carmav.exe (or 3dfx.exe, depending on the distribution) modified to optionally support Voodoo2 cards. It was programmed by a member of Stainless Software in his own spare time as a side project therefore you couldn't get support from the company.
It was successfully tested with Carmageddon UK (Zombie), Carmageddon UK Maxpack, Carmageddon UK Special Edition, Carmageddon US (Human Peds) and Splatpack UK, but I can confirm it works wonders for Carmageddon US Maxpack as well.
Presumably the reason it doesn't require the CD to be in the drive must be the complications that would have resulted from retaining the CD protection for all those versions. Guess he removed it altogether.