It is also made clear that there is a strange dual card cap.

Me:
5.7ghz
2x 275 STOCK = 1750 Nature

and at 1100core each = 1750 Nature. No increase.

Massman suggested it is a CPU limit.

But suicidephoenix has the same problem, 850 core on 280's in sli. and overclocked he gets same nature score at 5.9 cpu.

So something is up