Got a Sapphire 6950 1GB, unlocked, O/c'd to 900/625 or 925/625 running @ 1.1V
Stable at both 900/925, is okay 950 (more stable when increased to 1.2)
1000 crashes @ 1.1, stable @ 1.2
900 = 385Mhash
925 = 398Mhash
950 = 406Mhash
1000 = ~417Mhash (not sure only used at this speed for a couple of hours)
Can I ask what miner and flags you use for those rates?