ati-5870-furmarkOver at Legit Review they put the new ATI Radeon 5850 and 5870 through some benchmarks with FurMark and catalog the results on their site.  For example, simple rendering speed:

Benchmark Results: FurMark gives us some interesting results. Neither CrossFire nor SLI systems scale, so this benchmark is really only good for looking at the single GPU cards. The ATI Radeon HD 5850 was ~22% slower than the Radeon HD 5870 as seen in this benchmark.

They also compare temperatures (at idle and load), power consumption (at idle and load), and performance in various games.

via ATI Radeon HD 5850 CrossFire Video Card Review – FurMark 1.7.0 – Legit Reviews.