40 FPS is just fine for your card.
i wouldn't expect a 550ti to be a lot more better than that.
ofcourse your cpu isn't top of the line but not as bad as people in this forum will have u believe
and for ram. u stil have ddr2 ram!!!!
ddr3 is almost at it's end!
i say u wait until end of this year or next year start and get a new cpu+mobo.
by that time 4th gen i series and ddr4 will be out.
and for the orignal question your card is fine that is the performance it was ment to give. considering a few bottlenecks u have.