Additional Comments: I would like a quiet PC. This will be my 4th build, my first significant attempt at overclocking (but not to extreme levels). Last build was a MSI-6570 (K7N2) MoBoard, Athlon XP, 8x AGP, ATI Radeon HD 4600 system (circa 2004).
Build looks great to me. I like the PSU choice alot and can say for certain that the Mugen 2 Rev. B is fine for a 2600K @ 4.5Ghz. From what I have seen the Mugen 3 is a bit better than the Mugen 2 it replaced.
The difference in those 2 cards is the clock speed 900-1800-4200 vs 830-1660-4000 for the cheaper one. For $5 go with the overclocked one.
4.5Ghz should be a very easy overclock for that system. Just keep your voltage under 1.4v. If you have a good chip it will be more like 1.3v. My 2600K does 4.5Ghz at 1.32v but the 2600k is a bit more power hungry because of Hyperthreading.
I bought half of the above items last week (the ones with newegg rebates). I put in an order tonight for the other half. I should be assembling it by Friday and will update with comments on how it works. Thanks for the views and thanks to anort3 for the comment.