I am still new to overclocking, but if you have a good aftermarket CPU cooler (HSF) and have downloaded some system monitoring software and stability tests, you are ready to get started. I wouldn't bother with OS or windows based overclocking software, read your manual and use BIOS.
I have a pretty average Q9550, if your multiplier is set to 8.5 then it is at the maximum value. The only way to overclock is to increase your FSB Freq or b clock (stock is 333 mhz). The current overclock I am working on is 8.5x460=3.91 Ghz. and I have increased my CPU vcore to 1.35. As you increase your FSB speed, you will have to decrease your RAM speed to run around it's stock speed. On my Gigabyte motherboard it is "MCH frequency latch".
The maximum temp for the Q9550 is 71.6c, (I use 65c as my limit) and the max CPU vcore voltage is 1.3625 volts.
If you are using a stock CPU cooler, you will top out in CPU temperature at about 3.4 ghz, with a good cooler, I am at 3.91, and still fiddling.
Just for fun here is a shot of my system with a new cooler. I replaced a AC Freezer 7 Pro rev 1 with a CM Hyper 212+. I am very happy with it and it allowed me to get another 300 mhz out of my Q9550. Now running at 3.91 Ghz 24/7, nice and cool.
If you are using the CM V8, you shouldn't have a problem.
(those are 2 XFX HD5770s, and 8GB DDR2 800 OCZ Blade RAM @920 mhz 2.2 volts, we have very similar systems)