For my old K6 system, Voodoo3 had no problems playing DVD with 300MHz CPU using ATI dvdplayer 3.1.
But, when I upgraded V3 to a GF2 MX, in some games that use T&L, performance doubled compared to the V3.
In all games, performance with GF2 MX was as good or better than the V3, even when using Glide.
With such a poor CPU, performance is easily maxed out. (ended up bumping my K6 up to K6-2+ 450@600MHz).
However, what you end up with is the ability to run at higher resolutions.
With the V3, if an old game played at 800x600x16 @ 25fps max, using the GF2 MX that same game may get 30fps
at 800x600x16. The advantage with the MX is you can crank up the resolution to 1024x768, and it still gets 30fps.
Last of all, with the V3 you are stuck using max 16bit color and 16megs.
Some newer games require a video card that supports 32bit color. (LinksLS, Myst III, etc).
While a 300MHz machine won't handle 32bit well, at least you CAN run the game, unlike owners of the V3.
Links LS Golf sim's requirement for a 32bit card was the last time any 3dfx card saw my machines.
I have a friend with a Compaq in the same position. He at least has a 1200MHz Celeron.
So far, looks like the best bet for price/performance is GF2 MX 400 PCI at around $70.