I'm using a Gigabyte EP45-DS3R motherboard.
I've got an OCZ Vendetta 2 heatsink installed and I'm getting like 55c peaks with the processor all stock. I think I may have applied the thermal paste wrong but I'm going to leave that for another post in the CPU section.
Alright, since my PSU can run a 275/4890 I'm having trouble deciding between the two... in most benchmarks it looks like the 4890 outperforms the 275 (at 1650x1050, which is the closest to my monitors 1440x900), but just by a little margin and the 275 runs cooler and uses less energy. I don't plan on crossfiring (even though my mobo supports it), so I'm not going to choose ATI over Nvidia because of that. It also seems the 275 handles AA better. The price difference is virtually nothing ($10) so that's not a factor. Which should I go for?
From what I read the 275 runs much hotter but is more quiet. In load it reaches I think it was near 90 degrees, whereas the 4890 is louder but is more cool. I forgot what temperature. If you're into overclocking the 4890 has alot of headroom. I'm sure you could find a 4890 for a bit more than $10 cheaper as well..
Before making your decision read up a couple more reviews on both gfx cards since it seems what you read is a bit biased..