When testing with Left 4 Dead we see that at 2560x1600 the HIS Radeon HD 5850 is 15% faster than the GeForce GTX 285, while it is also 15% slower than the Radeon HD 5870. Furthermore, the older Radeon HD 4890 was 27% slower than the HIS Radeon HD 5850 at this extreme resolution.
In Resident Evil 5 the Radeon HD 5850 again works out to be about 15% slower than the 5870. More importantly, however, it is also an impressive 23% faster than the GeForce GTX 285.