This is kind of a silly question, sorry.

I have a spare brand new seasonic platinum 660w psu. Now I am planning on building a little litecoin mining rig with two 7950's.

I do not plan on adding anymore cards to this system...Most psu calculators are suggesting around 800+ for what I'll be getting. I think I could trim it to 650 or so if I
don't use an older 7200 rpm hdd and do some sort of flashdrive or ssd though. Do I need to stay very close to the wattage for mining or am I going to be ok with the seasonic?