I have a far worse graphics card than you - an old GeForce 8600GT with 256Mb memory, 2.6 Dual Core, and 2Gig RAM.  I have no problem with frames/textures on ths 757 (albeit a 2-3 second load time on the VC). Nor do I have issue with FSX set at quite high settings.  

Unless it is a combination of hardware that works for me, there's always something that affects performance, even the littlest detail.