Well just do it until your temperatures are as high as you are comfortable with. I try to keep the temperatures under 55 degrees at load, but that'll really heat up my room so I usually try to run it a lot slower unless it gets cool enough to run it at full speed.
With a locked multiplier you'd have to go for a max CPU and RAM overclock at the same time. You'd want to have high chipset and RAM voltages, high timings, and moderate CPU voltage. Then when it gets unstable, increase the CPU voltage. When you get to the highest FSB and CPU speed, try to reduce timings and voltages. Basically you want to get everything as fast as your system can handle, then tone down the stuff that restricts how fast it goes (like voltages and timings)
The timings are in the Advanced Chipset Config. It's called something like that. The FSB/RAM ratio controls the speed difference between FSB and the RAM. Like if you have a FSB of 200 and your ratio is at 5:4 then the RAM is at 160. For AMD systems you really shouldn't touch this, running it out of sync (same thing as running it in anything but 1:1) will decrease performance.