It's been a while since I used Adobe premiere, but I found that many things could not be hardware accelerated by a gpu, leaving my cpu to do most of the work, most of the time. I wasn't even able use the hardware acceleration on my gpu to help with 4k video playback, so it was choppy on the weak cpu I was using at the time. If i were to use this program again, then I would prioritise the cpu first, but still get the best gpu possible.
Maybe there have been a few changes since I last used this program and hardware acceleration is being used more?