Problem solved
After having known issues (horizontal corruption when scrolling in Safari [often] and color frenzy after starting Quartz Extreme applications [seldom]) I had the logic board of my Penryn MBP replaced.
Nothing else has been changed, same OS installation.
The problem is gone!
Even hard tries to reproduce the problem (cold & heat cycling, excessive GPU usage) have not been successful. Everything is fine now. Don't mess with false advice and ugly hacks to get around those problems. It certainly IS a hardware fault and Apple will replace it if you insist.
After having known issues (horizontal corruption when scrolling in Safari [often] and color frenzy after starting Quartz Extreme applications [seldom]) I had the logic board of my Penryn MBP replaced.
Nothing else has been changed, same OS installation.
The problem is gone!
Even hard tries to reproduce the problem (cold & heat cycling, excessive GPU usage) have not been successful. Everything is fine now. Don't mess with false advice and ugly hacks to get around those problems. It certainly IS a hardware fault and Apple will replace it if you insist.