That's a stupid question. The V5 is superior in just about every way.
MX's are seriously bottlenecked by the PCI bus due to the added geometry being sent to it, because of the T&L engine.
Even with on the AGP bus, the V5 is a much better buy than the MX.
The only thing I'd worry about is since 3dfx is dead, they won't be providing any more drivers, but the lastest betas are incredibly stable and won't cause you any problems.
/me votes for (ex)3dfx
Edit: LoL, BFG pretty much said the same thing I did. Bastard.:|
