Yes the 4200+ will be a slight bottleneck even up to 1600x1200, but as has been stated already the effects will be very minor above 1280x1024. I'm currently running an overclocked 5000+ @ 2.8ghz (I upgraded from an X1900XTX) & my performance has just about doubled in every game I play, so even though your cpu is slower then mine, if your current GPU is slower then my XTX was, you should see similar gains.