another option is to underclock by 50-100MHz (lose 200-400GH) and you will have about 50-100W less heat to deal with, and can run the fans a bit lower.
Im currently at 16% fans on a B8, with 61-66C temperatures and set for 4.45TH. (the -1C intake air helps)
IN my close to free power 1 s-7 limit setup.
I run at freq 500 or 4000gh fans are at 30% temps are 62.
THis is my friends office.
I get 1 15 amp break to use, I have to use 120 volt power and keep the noise okay.
So far so good. While many would say you are losing 800 to 900 gh I say I am paying 2.66 cents per kwatt at his place. So it is a nice setup for now.
I have some more space an may try to use some ductwork in his place. so I could go up to 4400 or 4600 gh.