1.5mm is used for the entire Strix PCB; GDDR6, chokes, every component on the Strix PCB = 1.5mm according to the response I received from an ASUS Support Rep who allegedly 'spoke with the engineers' before returning with an answer, which I later verified after physical disassembly for a much-needed replacement pad. I went with an affordable Arctic pad (7w/mK) for a short time before my curiosity compelled me to try the pricey Fujilpoly Extreme (11w/mK) and recycle my Arctic pads by migrating them to the rear of the same components on the backside of the PCB toward the backplate. I hope it may help to passively dissipate a tiny bit of extra heat from the components, but considering the Strix 2080/Ti backplate rests on standoffs and doesn't make proper contact with the PCB to begin with (nor does it have thermal pads installed in stock configuration) I sorta doubt it. There really aren't any significant gains to be had from replacing thermal pads alone unless you are need the extra bit of conductivity for whatever purposes in which case you may be able to get away with 1mm pads a thinner is better for conductivity and by that point you should just spring for a block and build a loop.