Your system bus is the speed that everything on the system communicates at, often referred to as FSB.
If you raise it, you raise the overall speed of the system including your CPU.
Your RAM runs at the system bus speed unless you employ a FSB:RAM ratio.
If you don't want to overclock your RAM, use this ratio to keep your RAM running at 200MHz when you increase the system bus.
ie. if system bus speed is 250MHz then your ratio would be 250:200 ::= 5:4 to keep your RAM running at 200MHz. (A theoretical ratio for an example).
But since your RAM needs to communicate with your system bus, if it's working on a ratio, it's not going to be the fastest your system can go because your RAM can't communicate with your bus on every cycle.
ie. at 5:4, the system bus lines up with the RAM at every 5th cycle.
This will increase your procesor speed, but it's not making the most that your system can provide.
BUT it is saving the very real possibility of your RAM frying itself because it's likely you'd have to raise the voltage to your RAM (vdimm) in order to let it run at faster speeds.
You could also overclock your board (which is good for it) by decreasing your multiplier, increasing your FSB, and keeping your CPU speed at the stock, again, employing the FSB:RAM ratio if you dont' want to overclock the RAM.
The agp frequency is good at 66/67, this will keep your video card running at the same speed while the system bus increases.
Read up before doing any changes though, and understand what you're doing.
Another thing to be aware of is your HT ratio, which is probably 5x, you'll need to lower it to 4x when your system bus is 200-250MHz, and to 3x beyond 250MHz.
HT x system bus =< 1000.