none of these will be good in games but the 250 is a better card. It will use more power but give better performance. The 250 is just a 9800GTX+ rebadged.http://www.gpureview.com/gts-250-1gb-versus-9800-gtx-review-article-772.html
I looked quite a bit and found no direct benchmark
Same here, but thank you very much for your help.
The shop, I bought my computer, tried to replace my broken GTS250 with GT640. I refused. Worst thing is that they got money for my old card, which wasn't repairable and tried to give me cheaper card then the GTS250 cost 2 years ago. I hate this!