On my 2012 rMBP it's the GPU that feels the heat (no pun intended), the CPU does fine more or less. But since the two are like conjoined twins, you're bound to get at least one of them throttling at one point or another, and sometimes even if you gimp the other chip with a third party tool.Tempting price but eventually not worth itThere is a large disparity between individual machines, I'm not going to look for this, I think it was on this forum, one fellow had really poor scores, did just that and saw substantial improvements. But my scores were not that far off of his after repaste, so the potential of destroying 4.9k (with Apple care and tax) worth of equipment does not justify the expected performance gains. In my case at least, apparently I have a good copy.
EDIT - I forgot, the GPU scores would not improve at all, it can maintain max clock without problem. CPU would improve.
Really, a metal-based TIM isn't all that necessary, since heat trapping eventually takes place anyway with a closed lid. A high quality paste can do wonders in some instances, since Apple's application is luck of the draw I'm afraid.