Depends on what you mean by "modern games." If you're buying off eBay, just grab a GTX 260 or 4850 for $20-30 and that will be twice as fast anyway. If you have a bigger budget, go higher. Multi-GPU is never a good idea as long as there's a comparable single GPU solution.A friend of mine still uses a 9600GT as his main graphics card, but he's thinking of getting an upgrade. Would it be worthwhile for him to grab a second one cheap off eBay and going SLI? Do old generations in SLI still tend to get decent performance in modern games?