I have a e5200 overclocked to 3.5Ghz and 4Gb or RAM, can anyone estimate for me the performance hit I would get by using an ati 5850 due to processor bottleneck, if any at 1680 x 1050?
Well, with an E5200 at 3.5GHz, I don't think there will be too much of a bottleneck at that resolution (I feel there would still be a few minor bottlenecks). However there will be on games which use three or more cores.
It would depend on the game. But given the i3 can run most games with a HD 5870 without much bottleneck, you'll be fine-ish. It'll bottleneck from the lack of L2 but that's about it.