Q: I'm debating on whether I should get one 9800GX2 or two 8800GTSs in SLI. I have heard that two 8800GTSs perform better than the 9800GX2.
A: In terms of performance, the GX2 is faster. The cores used in that card are similar to the ones found in the GTS/GTX. In terms of clock speeds, you can think of them as either overclocked GTS cores, or underclocked GTX cores. A single GX2 should be a bit faster. In terms of price, its a wash. The GTS cards can be had for ~$160, so two of them should be around $320. There are a few GX2's for about $300, but many are still closer to $400. Its going to depend on whichever is on sale when you buy. Another, dare I say better, idea is to CF two 4850s. These cards are also around the $160 mark, but are more powerful then the 9800GTX. Two of them should be more powerful then either SLI'd 8800GTS, or the 9800GX2, while costing about the same. If you already have an SLI motherboard, obviously this isn't for you. If however you are building a new machine, this is the better way to go. (you'll even get to avoid the troublesome Nvidia chipsets and stay with the P35/45, X38/48.)