I currently have an Asus P45 board with a E2180 running at 3.2ghz.

I am thinking of upgrading to the Q6600 which I heard can get upto about 3.6ghz on air.
Other options are the 45nm Q9 series. However, I have heard these are less tolerate of high volt even thou they do run cooler.
I am hearing 3.8ghz for Q9550 and 4ghz for Q9650.

The Q9650 is unlikely as it is so much more expensive but then again this would be the last possible CPU upgrade on a redundant format so I am tempted to get the best. What would you guys recommend bearing in mind there is about £60 difference in price between the Q6600/Q6700 to the Q9550?

1. Are there different stepping of the Q9550 I need to be aware of? I notice some CPU is designated Q9550S with a higher price than a normal Q9550.
2. Are there other Q9 series that are also good bang for bucks overclockers?
3. Electricty saved should be negliable but bearing in mind Q9550 need less volt would it last longer or is the reverse true because it have less volt tolerance than the 65nm when overclocked.

Anything will be an improvement over your current setup. I would be inclined to think that when overclocking, you won't get £60 worth of extra performance by going 45nm. It's all old hat compared with the current range, so why not save the extra cash.

The Q9550S is a lower power CPU (65W), but I doubt any extra overclocking ability will justify the extra cost compared to the standard Q9550 (95W).

In any case at the prices you mention I'd go with the Q6600/Q6700, the Q9550 would be worth £20 extra but not £60 imo.

If you can get hold of a Q6600 try to get a G0 stepping variant as these run cooler, mine runs at 3.2Ghz (400 x 8) continuously but I occasionally bung it up to 3.6Ghz for a bit of benchmarking.

HSF is an Arctic Freezer 7Pro, cost about £12 when I got it over 2 years ago.