yes at first i also thought a bad mount , but i touched the heatsink but couldnt do that for more than a second . So i assume the mount is OK .

my card runs 860mhz core with default cooler . above that my pc will hang (no artifacts seen ever)

the mem bandwidth of the R600 cards is massive and thus going above 999mhz will not give you any benefit at all . above 999mhz , the mem timings get slower people say .