I dunno if it's 24/7, I don't really care about 24/7 stability, I run stock 24/7. But it was stable in OC scanner @ Heavy for the 5 minutes I ran. It was also fine through 3dm11 @ 990, or 995.. Can't remember, I'll get the link and edit it in.
Edit: Yeah it was 990 stable through 3dm11.
http://3dmark.com/3dm11/2435613 Edit 2: Also forgot to mention, VRAM is good at stock voltage up to like 2300 at least, didn't go higher than that.