I use to be a fan of OCZ, but lately their quality has seemed to have dropped once they started mass producing everything in larger quantities. I reccomend the corsair line of power supplies. I purchased the 620W that has modular cables. Very handy and keeps everything clean. Highly rated among it's users and nearly whisper quiet.
Corsair HX 620W Modular Power Supply w/ Triple +12V
Is there a reason you are going for a quad core? I picked up a 3.0 Ghz core 2 duo 45nm that works perfectly. Not a lot of use for a quad core at the moment. At least not until more software utilizes it.
As well, I would try to get 8500 memory instead of 6400. A little faster, but pricier of course. I use the Crucial Ballistix 1GB x 4.
Great case selection btw. Antec makes extremely durable ones with lot's of room for expansion. I know what you mean about the aluminium, mine must weigh at least 40 lbs.
My ASUS P5K has been rock solid. Unfortunately I can't tell you how it is with overclocking and/or raid since I haven't tried either yet on my system.
As for building it yourself or having a ME tech doing it... I would have them assemble the motherboard with the cpu, fan and memory. They will usually do this for free and is only a 10 minute wait, and they even run a quick test on it. Then all you have to do it mount the power supply, drives, and motherboard into the case.