Most likely the GTS250 is close to the max your CPU can keep up with as well.
I still have a lot to learn about what components will be compatible with others.
What do you look at to determine what the CPU's limit for a gfx card would be? I have an AMD 64 x2 athlon 5200 or 5400 which ever one is the 2.7ghz processor.
I will put the computer specs in my sig tomorrow to make this easier.