Finally found a reliable source for trying my hand at overclocking my Dell XPS630i (got a bit snake-bit right after buying this machine with a BIG screw up on my part). HOWEVER, I'm now running a Quad Core 2.4GHz Q6600 stably at 3GHz (a 25% boost)! FSX runs FANTSATIC!!!
Initially started out with a modest overclock to 2.6GHz (found the settings at anandtech) . Ran stable, but I noticed my multiplier was shifting between 6 and 9 (using CPUZ) - which significantly interfered with performance. Did some more looking and found a great site for XPS630i users;
http://www.my630i.com/
Great section on overclocking using BIOS changes allowing for a direct boot up to 3GHz. I'm not going to mess around with going any higher, as you have to use NVidia control panel after each boot-up to set higher speeds (and it only nets an increase to a stable 3.2GHz). I must say, it's like a getting new machine for free. Don't worry, I'll be cautious. Any system instability and I'll back off a bit.
One last thing - I've read in various posts about 3GHz being the "sweet spot" for FSX. Based on my results, I'd say I have to agree.

http://www.my630i.com/
Great section on overclocking using BIOS changes allowing for a direct boot up to 3GHz. I'm not going to mess around with going any higher, as you have to use NVidia control panel after each boot-up to set higher speeds (and it only nets an increase to a stable 3.2GHz). I must say, it's like a getting new machine for free. Don't worry, I'll be cautious. Any system instability and I'll back off a bit.
One last thing - I've read in various posts about 3GHz being the "sweet spot" for FSX. Based on my results, I'd say I have to agree.