coderunknown
Retired Forum Mod
No Pulsur it is not true. 2 5770 in crossfire is better than HD 5850, but not better than HD 5870. Just checked the guru3d review. There are also some simple reasons also
a single 5770 has 800 stream processor, 40 texture unit and 16 ROP unit with 128 bit memory bus.
a single HD 5870 has 1600 stream processor, 80 Texture unit and 32 ROP with 256 bit memory bandwidth.
So doubling a HD 5770 will just match the Stream processor, texture Unit and ROp unit count of a HD 5870.
Now it is a proven truth that, 2 cards in crossfire, never doubles the performance, it is near to double, say 1.XX time increase in performance.
secondly the The motherboard, when in Xfire mode will operate in X8 mode, reducing the GPU bandwidth. So single HD 5870 cannot be beaten by 5770 is Xfire, but it definitely beats HD 5850. The negetive points are
increase in thermal and noise level as well as in Power requirement.
You are also closing the option of adding another card without selling oe of them.

about X8 mode. is HD5770 enough powerful to use full X16 bandwidth or say X8 too less? i don't think so. X8 should be enough for it. X16 will be a better but X8 Xfire won't affect performance.