the 4870 reference cards crash in intensive games like crysis, crysis warhead, unreal 3 gta 4
it depends on shader complexity used in the scene resolution AA AF applied core and memory clocks
heat can make the problem even worse because you don't need to reach 83A as the vrm's get get hotter the limit goes down ,i made my card crash in OCCT gpu test 600X400 window shader complexity 0 when it spiked repeatedly to about 78 A
idk if there is such a thing as vrm aging but that could make the things even worse.
crysis default gpu benchmark reaches about 60 A on 1600x1200 (default clocks) and more shader intensive scenes like the battle on the boat get the vrm's even hotter and combined with even higher vrma load end up crashing the card ---i have experienced this a few times .