Ok, well, I am sort of leaning now that despite the reported temps it is the cooling on the VRM modules that causes the cards to fail at higher volts. I was benching/stress testing with Crysis and I noticed that with the fan at 90%-100% I can get stable 875/1185 but only if I am running the fans so high. Drop the fans to say 50% and the test freezes. The volts needed for that clock are ending up to be 1.45V core and about 1.64V memory. Either way, I am pretty much convinced now that the 4870 XOC BE does not clock any higher than say 835/1150 on stock volts. Indeed, to be generally stable you need not go past 825/1125. Pretty lousy if you ask me for a card that states should be able to OC to 950/1200.
Yeah, maybe you can do 950/1200 with LN2 and about 1.6V on the core and another 1.7 on the memory. With air-cooling the best one can hope for that is true rock-solid stability (no ATITool artifacts, any game continuous 24/7) is about 850/1150 with roughly 1.35V core and 1.6V memory. Of course, as you can tell volt mods are required. Damn lying Diamond. They may have as well put 2000MHz max core speed and 4000MHz max memory, it would be just as realistic as the current CCC OverDrive limits for the 4870 XOC BE.
I now officially give the (3rd) 4870 XOC BE I tried and the whole line a big fat
Oh and for Diamond and their lousy lying.