Yea I've got the large textures happening on my V5, you really have to use 32bit colour to get the best effect. Oh and you need to use Geometry assist in the driver options to get it to work at all.
As far as speed differences go there isn't a whole lot that I could see, I use v-sync at 85hz on my monitor, and a lot of the time it just sticks there in glide or D3D, except where the scene complexity rises and the cpu limitation creeps in (if you can call a p3700@980 a limitation)
Overall I'm pretty impressed with this, It's cool to gawk at the detailed textures, especially CTF-Face. It's not quite as smooth as glide, a few hiccups here and there, and a couple of graphical glitches, especially viewing weapons in fog, and the invisible flag in CTF.
It is ever so slightly unstable though(like UT is 100% stable at the best of times)
I'll still use glide to play on line simply for the stability and smoothness.