For your current hash rates with the 270's, how much power are you drawing? This is a huge concern for me right now.
I don't know off the top of my head as I don't have a power metter, but the 270s draw about 225W each, then the mobo, CPU, HDD, RAM etc etc adds up to be about 100W (below 1500W for 4)
OC=Overclock
PSU=Power Supply Unit
Wrong. They draw in around 150W (the 270x), and you can handle 4 at 850W.
No the 280x are not better than the 270x or 270. This is just plain wrong.