I've worked on a couple Xboxes as well. I've only seen one gpu related rrod Jasper. That should tell you something right there.
I've seen only one Jasper with an issue involving the GPU and that was because someone had used excessive Arctic Silver on the dies and it spread to the other components on the GPU causing a short. I didn't even think once to attempt a reflow once I found out it was a Jasper. The customer brought it in and said it had red light issues, as soon as he passed it to me I checked the power socket and said, this is probably your power supply or a hard drive issue, he said no, disagreed with me, who knows better out of the two.. Well he was right, it was not the power supply or the HDD, it was the moron who over indulged with the AS5. Anywho, once opened, I explained the fault to him and only charged for a "cleaning & thermal paste renewal", which I charge a mere $20, so he was happy, more than I can say for his cousin who put the AS5 there.
I can tell you one thing for sure, I have been repairing electronics for a long time, out of all the Xbox 360 consoles, I have only seen ONE jasper console that was red ring because of the motherboard (was not even a BGA related issue), that's like 10 year, jaspers been around for only about 6-7 years out of the 10, I think anyone will agree that Jaspers are the best board quality. I have seen many Trinity consoles in for red light issues though, been they have been around for less time and Ive seen more of them, I'd have to say Jaspers are better, I do think Trinity's are better than Corona consoles though, based on the amount of consoles I see broken come into my shop