I have the Q6600 G0 stepping with Zalman 90mm air cooling and can't get it stable over anything but stock (2.4GZ). Pisses me off but I have seen similar posts. Can you post your settings? BTW, I have it on an EVGA i680 MB. Should have gone with the Gigabyte P35 MB.
The cheapest I've seen the E8400 sell retail is $199 @ Micro Center (currently out of stock, however). I can't believe the deals you can sometimes get at that B&M store...unreal. Strongly recommend the Quad cores for future longevity (Q6600 SLACR in particular due to price and O/C potential). If you are not in an absolute rush, perhaps wait for the Q9300's. I'm getting ready to put this new build through it's trading paces. Multicharts is running like some kind of miniature dos script... system doesn't even flinch with a slew of live tick charts. So far so good...
Most of the instability problem are due to memory timing and/or CPU multiplier matching. Have you tried decreasing the CAS by 1 step?
MultiCharts is particularly efficient with multi-cores... the more cores the merrier. MultiCharts can farm out each chart window to a core. If you have 4 chart windows open, each chart will have its own core to work with !!! You don't even need to OC the CPU to make MultiCharts sing.
In order of importance, I would look at memory timing, motherboard chipset setting (default it) and then CPU cooler. The Q6600 G0 SLACR should be able to do 3.0ghz no problem with good air cooling. When initially attempting the overclock, you are using CAS 5-5-5-15 type setting, correct? What kind of cpu temps are you reading? Not familiar with the i680 chipset, so don't feel comfortable giving out advice. But I will say, yes the P35 Gigabyte as well as the Abit I35-E are very proven boards with O/C'd Q6600 and currently very inexpensive (~$80-90 shipped of top of my head). Both have seen a slew of both bios and board revisions, and will prove rock-solid stable for critical situations like trading. The only reason I opted for the newer X38 is because I run 4 24" Samsung LCD 245BW's and wanted them powered by two PCI x16/2.0 capable slots & v.cards. My cycle has typically been 2-3yrs before upgrade, and hope to keep it like such. If one is willing to spend the dough and wants to try the X38 chipset for their Q6600, I would opt for the Gigabyte X38 D6Q, not the discontinued D4Q. Asus Maximus is also an option, but have to admit as a long time Asus lover, their quality has gone down hill and customer service always a serious PITA. The best air cooling for the Q6600 is the Thermalright 120 Ultra Extreme closely followed by the Tuniq Tower (which is what I run). Don't let the silly enthusiastic names fool you, they are "very" quiet. This coming from someone who used to build the PC's for a professional audio mastering studio I used to work at back in the day.
On better thought, set timings to auto, and run it 1:1. Also, what power supply are using and wattage? Q6600 is somewhat of a power-pig. I'm running an Antec Trio 650W. Vcore settings? Cooler properly mounted to chip...enough thermal paste and no wiggle? You'll get questions/concerned answered in a flash over at some 680i O/C enthusiast board. Just do a google search and you'll get some hits.
Not really. It's useful if you want to time your next upgrade or new PC purchase just like you wouldn't buy a stock now if someone tells you it'll get a haircut down the road.
Running timings on auto running 1:1. I have the same PSU (650W). I will try some of your other suggestions. Thanks.