Case fan will make a huge difference. Right now your case is like a oven.
90c on 6870 should be fine, but lowering it to below 85c is best.
My 6870 is at the 90c too, but its getting old and has a stock cooler.
90c on cpu's is very bad, get a new cooler. I had this problem too.
I had 5xc on idle and 8x - 90c in games. I bought a aftermarket cooler for the cpu, now its.
19c idle 35c in games, and i even OC it too.
As you can see it makes a huge difference
that'll help me sleep through the night