190 mining seems close since it is very hard on the card.
This is what Techpowerup got with the 7950shttp://www.techpowerup.com/reviews/AMD/HD_7950/25.html
AMD recommends 750 plus.
Now lets say the cards hit 200 watts each and the cpu is hitting 75(i know it has a TDP of 55)
Add in another 50 for everything else and you are just under 550 watts(as a high guess for a bit of safety margin). Now getting something a bit bigger never hurts and should be good for the unit to not work too hard.
For a normal system I would go on the lower end, but since you are running hard all the time, I would go 650 + just to keep it stable.
AMD's 750 also takes into account higher wattage cpus and you do not even have a hard drive.