Bright Side of News reports the new ATI Radeon HD 5870 doesn't perform any better in Folding@Home than its predecessor due to software issues. The ATI client is based on the retired Brook+ and as this runtime is no longer supported Folders will need to wait until a next-gen version of Folding@Home comes out that supports OpenCL or DirectCompute.
However, the performance wasn't what we expected - Radeon HD 4870 and HD 4870X2 will both yield around 3000 points per day and we definitely didn't expected that Radeon HD 5870 1GB will join the club. In our measurements, different units showed that the number of points will vary between 1650 and 3150 points per day, dramatically lagging behind nVidia GeForce cards.
In comparison, Gainward's GeForce GTX 275 returns between 5400 and 7100 PPD - depending on how complex the units are. Direct competitors to Radeon HD 5870, GeForce GTX 285 and GTX 295 are simply leaving HD 5870 in the dust.