Hey,
If your looking to OC to 4GHz then I would seriously consider the i5 3570K and a Z77 (most people are getting 4.5GHz out of the 3570K without heat problems and some are getting as high as 5.2GHz before things start to become a problem), neither the Z68 or the Z77 offer much (if anything) in the way of an upgrade because Intel's next chip release (Haswell) will use a new type of motherboard with a new type of socket so as far as "future proofing" goes your better getting the latest and greatest allowing you access to the newest tech available now and for the next few years.
I would also advise looking in to some good paste unless the cooler you decide on ships with some (a quick google search should let you know what people make of it). Although its not that expensive to buy a good brand anyway...
csgohan4 is right about the filters, I'm not sure if the 550D has them or not (the 650D does) but its worth looking in to - Its a really nice case though and would have been in my top choices for my new build if I didn't love the 650D like I do!
Good luck with the build though, it looks like you will have a solid build equipped for several years of good gaming
Rookie
P.S. Oh and swap that Sandisk SSD for either an Crucial M4 or Samsung 830