The "reference" clock is 925MHz, and there is at least a 1Ghz board out there too (XFX)
Still a huge OC, i wonder how many Watts that thing is pulling (400 to 500 stock?)
By the way...
Quad 7970 Crossfire @ ~1500Mhz
http://kingpincooling.com/forum/showthread.php?t=1570