My experiance with the XTXH are the same as buildzoid. I have the watercooled Ultimate but my card is stable with the 100mhz step between the min and max clock. But i tried nearly everything to get the memory more stable past 2150 mhz. The only thing i found was to increase the minimum soc voltage up to 950mv in the powertable. My memory wasn't even stable at 2130 mhz with fast timings and with the increase of the min Soc make its stable up to 2155 with fast timings, higher min voltage gave me no better results. With more powertool from igor it's no problem to edit the powertable.
My experiance with flashing the xtxh to xtx cards ends in a non working card, and i had to flash it with a programmer.
Crossfire with a XTXH and XTX Card did not work for benching Timespy.