The 5200+ isn't that powerful, but its still a dual core at 2.7GHz so its not the end of the world. It will hold the 9800GTX+ back a bit, but it won't be horrible. 1440x900 should be alright, 1680x1050 will be stretch. The 5200+ isn't good enough for 1920x1080, so I wouldn't try that.
Although I probably wont go over 800x600 due to my current monitor size, (15in), I'll keep that in mind. If the amount of power the 5200 holds back gets really bad, would over clocking still be an option for me?
For that res, both the Video Card AND Processor are complete overkill. Take heart in knowing that you can safely move up to a 19 or 20 inch monitor before you have to worry about any bottlenecking going on.
8x6? Wow, thats pretty low/bad. If thats your res, you'll be fine. Bottlenecking won't be a problem until you try to do something that a single thing in your computer will start holding other things back. In your case, your bottleneck is your monitor. It prevents your 5200+/9800GTX+ from performing to their full potential. I'd worry more about upgrading your monitor then your GPU.