Re: FX 5600 or Voodoo5 5500?
For this objetive, the 3Dfx Voodoo 5 5500 with no-official 3Dfx drivers. Back when I had the 3Dfx Voodoo Banshee I got some good drivers that added support for OpenGL perfectly for it, and even the performance improved in Glide of DirectX applications. Try searching setupgl... it's the name I think the site of some of them had.
__________________Intel Core i7 920 @ 3'80GHz (Scythe Mugen II)
MSI GTX560 Ti Twin Frozr II @ 960/1920/2280
Asus P6T BIOS 1408
6 x 2GB Kingston ValueRam DDR3 1333 @ 1520
Nox Pulsar 750w / Windows 7 Home Premium SP1 64Bits