I have a e8400 oc'd to 3.6ghz on the stock intel heatsink fan and i was wondering
would it bottleneck a gtx 460 or hd 5850 at 1920x1080 resolution?
No that is a very fast dual core so you will be fine.
how about a 6870 and rolli i have another question on my other post
It should be fine with the HD6870 as well. The only time it will be a bottleneck is when games are multithreaded which is very few. I see in your other post that you are upgrading from HD4890 which is still a powerful card. Anything less than a HD6870 would not be a notable upgrade http://www.techpowerup.com/reviews/HIS/Radeon_HD_6870/29.html