Be careful with the CPU upgrade - an X9000 may work but that CPU draws 44 W, vs 35 for the one you have. That's a 25% increase in power draw - which the system may not handle. The T9500 is a 35W CPU and should work fine, though.
The other thing to consider is that the GPU will remain the same (it cannot be upgraded), and that if you have a standard hard drive, it will remain the limiting factor. If you do just one upgrade to the system, the biggest overall impact you can make on the system won't be the new CPU - it would be to replace the hard drive with a solid state drive.
