Immagikman,
A couple of words about the 9800gtx. Please forgive me if I'm telling you some things you already know, I'm pretty new at this stuff myself.
1. The fan bug. There is a bug with nvidia drivers/bios for the 9800gtx that when it gets over 60C the fan reverts to an automatic 35% speed. This bug trumps any software fan control that I've seen. The only current fix I've found is actually modifying the wiring on the card, which is beyond my willingness to mess with. Nvidia, and EVGA have both recognized this problem and they have said that it will be resolved in the next round of nvidia software that's released. I would advise not OC'ing the card for anything other than short benchmark runs, until that's resolvled.
2. The good news: The card can OC like a champ, and once the fan can be set to stay at high percentages, I think the cooling is going to be more than adequate. I have had success around 810/1800/1200. I haven't been able to do any long time runs at those settings, because I'm afraid of the high temps, but it runs 3dmark06, and plays crysis with no artifiacts in the short times I've tried it. That OC, granted about 1500ish points in 3dmark06 for me.
3. Software If you are using the newest NVIDIA ntune software to manage your gpu clockspeeds, it works well for that, but please avoid the interactive bios tab for your MB, that can screw up pretty easy, I had to reset by jumper when I tried to use it. Noob mistake on mypart. EVGA has a nice tool for overclocking nvidia gpus. Rivatuner is a good tool. Once you find where the three clocks are, and the fan tab, if you're an ametuer like me, that's all you need. Any of the three softwares I've mentioned work fine for setting the clocks. I'm sure some of the other more experienced guys could probably suggest a few other tools.
4. For me the GPU seemed to be bottlenecked by my processor(Q9450) up to about 3.4 Ghz. I got about 4kof 3dmark gains going from stock 2.66 to 3.2, but the returns diminished between 3.2 and 3.4, and diminished even more between 3.4 and 3.6. 3.2-3.6 gained less than 1000 more points, most all of which were cpu score. I haven't tried anything over 3.6 because, again, I have a phobia of thermometers, and only air cooling. Bottom line is I think you'll get just about all you can out of the 9800gtx at 3.2 with your q6600, without worries of cpu bottlenecking.
5. I'm a noob, this post comes only from my personal experience with my current rig. I highly advise getting additional opinions on these issues, but I hope something above can be helpful for you.
Z.