notice a strange slow down on Bnet gameplay..

Spec:
Win7 Ultimate 64bit
i7 740QM (2.9ghz)
8GB RAM
5850m (Overclocked from 625mhz to 790mhz)
128GB SSD

When I play 1v1 with A.I, I get 50-60 FPS constantly on Ultra.
But when I play 1v1 on Bnet, on the same map, I gets only 30-40fps :/
I mean, It's 55+fps at the beginning when I play with A.I, is there any reason I can only get 30-40+ FPS on bnet, under same settings?