In moving to the Cosmos, I have not noticed an increase in temps although the fans in the Cosmos are really low CFM so I'm thinking there must be some slight difference. But, the Cosmos has more fans so who knows. I have stopped messing with overclocking until the fall/winter and am running Intel's version of Cool-n-Quiet on my E6420 right now.
The Cosmos is slightly quieter than my P180 setup was. Granted, the P180 was already very quiet.
The construction of the Cosmos is FAR superior to the P180. It feels SOLID and the quality is great. It makes the P180 seem flimsy and cheap in comparison. It is definitely bigger and heavier than the P180. But, because it sits on the floor on those metal bars, it is super easy to slide the computer around and move it (especially if you are on carpet like my PC is). Sliding around the P180 was always a PITA because the rubber feet would grip the carpet too much.
The way the side panels latch/unlatch is sweet and is much nicer than the P180. I had lots of problems with the P180 side panels. Getting them on/off and to stay in place correctly always seemed like somewhat of a chore. The little tabs on them broke on me twice. Antec was nice and replaced the entire side panel for me once. I didn't bother to ask the 2nd time and just made sure I had a screw installed to keep the side panel from popping open. The Cosmos side panels just latch into place with a 'click' and you're done.
The front door can be reversed but the stock (opens to the right) is perfect for my layout. The 4 USB ports on the top are great and much better than on my P180 (the ports stopped working last year on the P180 even though Antec had sent me some new ones a while back). The hinges and the magnet for the front door are super smooth and seem very refined.
I love the fact that I don't have to open the door to turn the power on and off. However, the blue (power/hdd) LEDs on top are a little brighter than I'd prefer.
My Corsair HX520 PSU worked great in the Cosmos with my DFI Infinity P965-S motherboard.
I love all the extra room you have to work with in the Cosmos. That and how easy the drives are to add/remove was one of the main reasons for getting the Cosmos besides the other nagging problems I was having with the P180 mentioned above. Plus, I wanted a different look and I really like the look of the Cosmos compared to my (original version of the) P180.