how much should speed 290 in quark?
12.4@900/1250
14@950/600 xI=1024
16MHs/955/800 xI=512

That's a 290"X", same over here..
ah, ok, mine is 290 without X

weird, because xI=512 is slightly slower for me... but I may be cpu-bound, because the cpu is ancient Core e2180 @2GHz, 2GB ram

Cpu has no effect, i have two Rigs with 290 cards, one had a regular Pentium and the other has an i5, same speed on those cards..
However, drivers, that's something that does have an effect!
If opencl dlls are in the folder of sgminer, then drivers are not important