I've never overclocked vid cards much but my mate & I stuck it to our gtx's to see who's could go highest. He has a gigabyte, me an asus.
His went up to 940/1050. Mine only 934/1050
BUT, our scores were way higher than yours. Your sm2 score is 500+ points too low, and your sm3 is a few hundred too low to. All up I got 13585 with:
E6750 @ 3.4
2x1gig patriot 6400
But as long as you are happy with it & it plays games fine who cares what 3dmark says