right leaving out a hd7790 and using a hd7970 is wrong since a 7790 is the cheapest gpu for btc mining based on hash /power / price.  


 A hd7790 is 300 hash for 80 watts at 1.1 btc  

 a hd7970 is 650 hash for 240 watts at 3.3 btc    


 at todays rates  the hd7970 makes about $1.55 a day   2 hd7790's make about $1.67 a day    and you spent 3 btc to get the hd7970 and 2 btc to get 2 hd7790's...  of course if you are short slots some will argue the hd7970 is better. in my case I sold off used hd7970's and replaced with hd7790's worked out well sell one used hd7970 and get 3 new hd7790's pretty good deal.