I have underclocked my card to 480 levels and managed a stable undervolt of -100mV (from 1150 to 1050). I might try something lower in the next days, but temps don't go over 70C now during benchmarks (before they were about 7C more).
Perfect i am glad that it worked for you. If you get two additional fans as intake below the gpu then you can put it up to stock clocks :)
I actually changed to 1306Mhz and 1075mV after a crash the day after. Temperatures are still much lower than stock clocks.
I will think about getting the fans, but the GPU support is very nice (especially since I need to bring the PC on the plane). By the way, would you remove the GPU or any other componenent prior to taking the flight? (I will keep it with me as carry-on).
normally people prefer to get cpu cooler removed as an example but in your case I think it should be fine since cooler is very small. I would maybe unattach gpu from the motherboard and it should be fine IMO