Is it overclocked?? I went from a Q6600 at around 3GHZ to a Core i3 2100 and it was an improvement although I moved to DDR3 and Windows 7 64 bit at the same time too(had Vista 32 bit and 4GB DDR2). OTH,a Core i3 2100 is in between a 3.2GHZ to 4GHZ Phenom II X4 in most games. The move was sort of sideways but my old SD37P2 was having issues after nearly four and a half years!
My Q6600 at 3GHZ could just about push an HD5850 1GB running at 925MHZ for the core(stock core speed is 725MHZ for the GPU) to 100% when playing Crysis2 under DX11.