try 24fps vs 60fps videos. is it worse, better, or same?
there used to be a bug where if you had premiere ui windows that overlayed across two monitors, premiere couldn’t playback fast. try removing all windows or playing back fullscreen.
you could also try the free davinci resolve and do a little debugging in there just to see if its Premiere only or the actual eGPU drivers.
have you asked adobe if they have any ideas?