On mining efficiency:

One other thing that I've found with tuning the cards is to optimize for power efficiency. Make sure you get cards with unlocked voltages so you can do this. I've been able to lower the power usage of my 7950's from 225 watts down to about 175 watts under full load while still getting good hash rates. The cards are most efficient when running about at or below stock speeds but undervolted (.962v instead of stock 1.25v). You'll also need a kill-a-watt meter to measure power usage at the plug if you don't already have one.