Before we completed our testing, we spent a little time overclocking the HIS X850 XT IceQ II Turbo and X800 XL IceQ II Turbo to see what they had under the hood.  First we tried our hand with HIS' own iTurbo utility and then took things even further with the use of Entech's PowerStrip.

Overclocking The HIS X850XT IceQ II and X800 XL IceQ II Quiet Overclocking

HIS X850 XT iTurbo Clock Speed = 540MHz Core/1180MHz Memory  (520/1080 stock)
HIS X800XL iTurbo Clock Speed = 432MHz Core/1000MHz Memory (400/980 stock)

We were able to chalk up another 6-7% performance gain with the simple one-touch button interface of the iTrubo setting with these two cards.  As the old saying goes, "easy money"... But is there more headroom here?

X800XL IceQ II Turbo Max OC = 460MHz Core/1080MHz Memory
X850 XT IceQ II Turbo Max OC = 570MHz Core/1230MHz Memory

With a blistering 570MHz max core speed the HIS X850 XT is one of the most overclockable X850 cards we've seen to date.  In addition, the HIS X800 XL with its highest overclock is able to edge past even the GeForce 6800 Ultra in our Far Cry benchmark, with a 5% performance advantage over the flagship NVIDIA card and a 460MHz max stable core speed.