I agree with what DarkMajiq said.
You should keep testing other frequencies between 1100 and 1320 MHz. Try 1200, 1250, 1275, and keep testing it out until you find the greatest speed at which your computer will remain stable with the CLI. You'll still probably be better off with the CLI at 1100 than the GUI at 1320.
On my T-Bird 1400, I've tried overclocking to anywhere from 1500 to 1650 MHz. At 1650, I basically killed my processor, but was thankfully able to resuscitate back to life. Right now I've found that the highest stable speed I can get to is 1586 MHz (10.5x151). Anything higher, and it'll last for a little while, but it'll eventually blue screen on me.
It'll just take some patience and some tinkering to find your ideal overclock speed. Keep in mind that upping your FSB helps your SETI times more than upping your clock multiplier, but can make it more unstable.