I'm seeing 3780mhz out of an X6800 ES for 24/7 use. That's in an enclosed case with 1.50v and basic water cooling. One caveat is that I like lots of stability "overhead" and silent running for 24/7 settings. It will bench at 3.9 at 1.57v for hours, but it will throw a random error at 4ghz regardless of voltage. My Mach II would probably get me quite a bit farther, but my benching days are over.

Blazing fast anyways....just not a star. If you look you can find mediocre ES clocks. No one wants to post about them though