I have 1 x 5970 and 4 x 5850 (flashed to 5870) on one rig. CGMiner and Xubuntu 11.04 64b. The 5970 runs stable at V=0.95 E=710 M=150 & Mhs 324 per GPU. The cool core will go to E=720 but the hot Core will not take E=720 it needs 710 to stay stable. My room temp is either hot or hotter (tropical) and the fan run at 56% in an open frame rig.

There is a very good thread somewhere here on 5970's take a look. Thats where I got those settings from

Edit try here:- https://bitcointalk.org/index.php?topic=98901.0