My favorite sites in order of the ones I find do the best testing are Xbit, SilentPCReview, ExtremeOC, and SL Central. At the moment there's a fair gap between the first two and final two due to lack of test equipment, but all four have at least load testers. Tom's has a load tester, but they only measure efficiency with it lately. They used to have decent reviews, but not so much anymore.
I too get my longevity information by studying user experiences on several message boards. When a new model comes up, I usually spend a couple months waiting for the early adopters to report back on their investment and then compare with what I've been able to learn about the OEM in the past before making up my mind whether I want to recommend it or not.