Q6600's dont generally like going past ~3.5ghz - keep in mind these are 65nm parts - my Q6600 maxed out at 3.5ghz, and any board that will give you any increase will only be in the field of a few mhz - not worth the effort
8x vs 16x PCIE lanes wont make much difference with a Q6600
The fact is, I get instability crashes at 3.4Ghz regular, sometimes at 3.2 and at 3ghz im fine, Its my board limitating it, im fully aware of that, the 680i chipset is TERRIBLE.
(Im very attatched to my Q6600 I want it to be at its fastest before I replace it with a Bulldozer rig in 2K11)
Either way, im bidding now on a Gigabyte x48 high end board.
Hey dead, this isn't the advice you looking for but, like said already, a good q6600 will get 3.6 maybe a tad over on good air cooling. And that is pushing the voltage close to safe max if not to it's max.
If you can get a stable 3.3 or 3.2ghz, I really don't see the point in going through the trouble for a few hundred mhz. Even with a great mobo, 3.6 and beyond is not guaranteed.
From what I see your overclocking your ram, so it is definitely possible. In my experience it's always best to overclock one thing at a time. So maybe set your ram to 1:1 ratio, then start working on the cpu again. You can always tweak the ram after you have a stable cpu your happy with.
At 3.4 and above I don't think there will be any significant bottlenecking, and should be capable of running any game out there, flight sims being the exception, perhaps.
I think your Q6600 and a single 6870 will be about matched and give good performance at 1080P resolution.
Do you have enough ram? 4gb at least?
I don't think I would invest much in a system that is two generations old, going on 3.
There should be single card graphics solutions available for upgrade so long as you are using a single monitor. If you should go to a 2560 x 1600 monitor or triple monitor surround, only then wouldthe expense of sli/crossfire be appropriate.
Im gonna do some tweaking tonight. Its seems best to leave it and wait for bulldozer/Sandy bridge (depending on release benches)
Ill recycle my 6870 for my updated rig in 2011, im running 2 8800GTs atm and a single 6870 should destroy them for performance.
I guess you've saved me a good £70
To help clarify your situation, run these two tests:
1) Run your games, but reduce the resolution and eye candy to a minimum. This will simulate what will happen if you upgrade to a stronger graphics card. If your FPS improves, it indicates that your cpu is capable of driving a stronger graphics card to higher levels of FPS.
2) Keeping your graphics resolution and settings the same, reduce your cpu power. Do this by removing the overclock, or by using windows power management to set a maximum cpu% of perhaps 70%. If your FPS drops significantly, it indicates that your current cpu is a limiting factor, and that a faster cpu would help.