If you are willing to possibly trash your whole system continue with this task. You are correct. Your AGP and PCI devices may not go higher. On my system I was able to raise my FSB from the stock 200MHz (3.2GHz CPU) to 420MHz (4.01GHz) without raising my AGP or PCI clocks. This may be a function of your motherboard. My memory is spec'd at 400MHz.
Notice my CPUz Image. This is a better way of posting images. It won't stretch the page