I had a Voodoo 2 SLI setup for a while (and will again once I build my "classic" gaming machine. I grabbed a Creative one day one for $300, and bought the second for $50 from Creative when they were selling a ton of refurb cards.
I also had a friend with a single PCI slot Voodoo 2 SLI card. Now that was a big card. Basicially glue two Voodoo 2 cards togther, but insert a DEC PCI bridge chip in the middle.
It's a nice idea, but the peformance gains probably aren't there anyhow. 2 8500's may very well be slower then the R300. Two R300 chips on a card would be awesome, but ATI has to milk us rich gamers first with just a single chip card