Either or. At that price point, they're both decent cases...it just depends on what you want. It looks to me like the 650D offers better cooling with the front intake, but in my experience all Corsair cases are good quality.
I know this isn't what you were asking, but what's your build for? Are you gaming or doing video editing? If it's just gaming, ditch the i7-2600K and the 16GB of RAM...an i5-2500K and 8GB is fine. The money saved could get you an SSD for a boot drive.
I ordered a Corsair 550d a couple of days ago and just got it this day. The 550d gives you the option of good cooling or quietness , mix? While the 650d gives you extreme cooling. I currently have my 550d with all lids on and it runs quiet. I can only hear a swoosh of air from my GTX 460 1gb which previously on my NZXT Gamma made a turbine noise when on full load.
If you don't care about fan noise get the 650d
If fan noise makes you go mad (like me) get the 550d.
The 650d also does not have usb 3.0 front panel header the usb 3.0 is through cables going to the back of the motherboard. While the 550d has internal usb 3.0 header for motherboard. The 550d has filters on every intake while the 650d only has them on the front and bottom (psu). The 650d has a window and a hot swap area while the 550d has none of those.
I also recommend dropping that corsair 650 M and getting a seasonic 620 modular it's like 90 dlls on amazon. The psu is almost fully modular and it's higher quality than Corsair.