@vimal992: I tried it on different motherboard, still no luck, so that is not the case, even I bought new hd 4850 from pwoercolor 1GB, which runs pretty cool @50degree c max on load. on the same setup.
so visiontek cards are the real culprit. they are well known for overheating.
will give one last trying cleaning card and reapplying heat sink, miracles do happnen, didn't they?