Otherwise, Yeah, it's all about your case. How much noise it can dampen and how much air it can abuse
My miner is in the garage so it's not an issue. I've decided to let the 5770 run up to 85C, which puts the fan at about 92% (it's about 40C in my garage right now) That lets both the 5770 and the 5830 run at their max stable overclock.
I'm planning on a 2nd 5830 (if anyone ever has them in stock) and I think at that point I'll have to go to an open case.