Stupid Question
#1
Would 2 6990's be faster than 1 7990? thanx
#2
Yes, the 2xhd6990 is faster, but not much:

1x hd7990 @ ntlm : 32986 MH/s
2x hd6990 @ ntlm : 39151 MH/s

But you save the pcie slot and the power consumption