The 5830 is a turd. It's not any faster than a gtx 260, which was available for $99 the other day. These things will be $50 at newegg when SI comes out.
If your performance isn't up to snuff, grap another 5750 for xfire or get a gtx 460. If I were in your shoes I'd get the 460 because 1. it will give nearly 5850 performance on the cheap and oc's like mad, 2. xfire is still spotty and always a backup solution imho, and 3. you clearly prefer nvidia anyway.
You can't overestimate #3 either, trust me. I've gone back and forth over the years on my preference with both cpus and gpus, and right now is a bad time for me. I bought ati when everybody was dogging on them during the 8800 era, now I have an nvidia card because everyone is dogging on THEM. I don't really like intel that much, but in cpus there is no competition. I'm itching to upgrade my whole system right now and I can't find anything worthwhile to upgrade to. I'm sure fermi II will smoke SI so I'll just switch back to amd then I guess.
