Need hardware suggestions for computer upgrade

Currently, I have a Dell XPS desktop with the following components:i7 920 @ 2.678GB dual channel RamATI Radeon 5870450 W power supply1TB Hard driveBasically, I originally ordered this computer a couple years ago because I was sort of afraid to attempt building my own PC (I'm not too tech saavy). Of course I didn't realize until afterward that Dell's motherboards are specifically designed to deny you ability to overclock the CPU - the BIOS doesn't even have that option. I didn't gripe too much, 'cause it's still light years better than the previous rig and runs FSX pretty well. However, if I'm trying to fly in major cities/airports with complex aircraft, it's still almost unplayable if I want to have my desired scenery settings, especially with the addons I have, not to mention record videos. Lately I've reverted to switching back and forth between flying GA in FSX and IFR/heavies in FS9, but I just want to move exclusively to FSX now, and I think I'm on the market for an upgrade.I want to get the necessary stuff to be able to overclock my CPU (pretty sure that's what probably most determines how FS runs, right), but on top of that I think I might actually just dive in and get the 2600K along with the new motherboard, and a few other improvements - new case, liquid cooling, new power supply, and maybe another hard drive or two. (Almost a completely new rig I guess, haha!) This seems like a lot but I use my computer for recording music as well so I could use all the storage and power I can get. I'll probably just stick with my 920 for a while though, but I at least want to be able to overclock to 4.0 ghz.I'm still kind of stupid when it comes to this stuff so I'm just wondering if somebody could suggest to me what's necessary to make this happen? What kind of motherboard would I need? What else would I need to do in addition to getting the physical parts and installing them? (I can get a friend to help me with the overclocking part).I know this is a lot to ask. I've sort of googled and searched for what I can but just seek a more concrete answer.Thanks for any help.