Crossfire help again

Hi guys

2 x ATI 4890 DDR5 Cards
P7P55D PRO Asus Motherboard
8Gig Ram
Windows 7 (64bit)
i7 2.8Ghz Processor
1000 Watt powersupply

Everything installed and everything picks up. Crossfire enabled but Zero difference in ARMA II's FPS benchmark.

Am I missing something here?

In ther ATI control centre it shows both cards under hardware and crossfire tick is enabled, but when you go to overdrive (overclocking) function for example the drop down box only shows one card whereas I think it is supposed to show 2.

How can I improve performance? Surely another expensive card like this is supposed to make a difference?

Thanks