basically look at clock speeds and temps from reviews on overclocked cards
reference cards just look for the best warrenty
Usually tom's hardware charts are solving any issue i have the different manufactures are having different cooling systems and I can see this on charts some card has bit less C due to better stock cooler if I need to see someone’s better I go to their sites or I search in Google for a review and testing is easy.
for example in charts you see sapphire has less C temperatures then i went to the Sapphire's web site and i've seen they using a vapor-x cooling system i tried to find this cooling system to test it in my HD5770 but i didn’t find it somewhere i guess they don't shell it separately so is better to look this also.
Usually 1 year is enough if there is not a faulty build (sometimes it happens) then you will not have problems in the years after cooling system is very important issue to that direction and there are not so many cooling systems out on the market now for HD5770 to help us in that direction. His appears to the charts fastest but I bet always in the cooling system.