Hi Greg, and thanks for the post
Greg said:
Personally I am having difficulty believing that 2 5770's in crossfire can beat one 5870 in any of your test, after all even if crossfire scaled 100% then the 2 5770's would still be giving up half its memory bandwidth to the 5870 and at higher resolution and with FSAA enabled the mem bandwidth makes all the difference.
You certainly aren't alone. When I looked at the results after testing, I didn't know what to make of it, but regardless of how it happens, those are the results we saw, and I'm confident anyone doing the same test will see the same thing. Could it be the improved architecture over the previous generation, or improved drivers? I don't know, but given that we use the exact same test machine and fresh OS install before each testing, not to mention completely manual benchmarking (no timedemos), our results are what they are.
What's somewhat interesting is that our 3DMark Vantage results backed me up a little bit:
http://techgage.com/article/ati_radeon_hd_5770_crossfirex_performance/10
There's a wider variance at 1680x1050, but at both 1080p and 2560x1600, the HD 5770's in CrossFireX and the HD 5870 are scary close in performance... there's just a ~6% difference between the two configurations in the latter. For raw performance, the HD 5870 comes out ahead, but in real-world gaming, there are cases when they come out about even (it's easier to see differences when we're dealing with numbers in the thousands... not so much when talking about 40 - 50 FPS).
If I get a chance today, I'll load up that machine and test out both configurations again briefly just for the sake of it.