3.8 GHz @ 1.3v is pretty good, especially with the stock cooler.

Lightman, can you do me a favor? Try booting with the stock DDR4-2133 settings, copying over all the timings/subtimings by hand, and then slowly run the RAM speed up to 3200 MHz. Set vDIMM as high as you're comfortable with, though I would recommend 1.4v vDIMM and anywhere from 1.1v to 1.175v SoC voltage. Let me know how far you can get with that thing.

I did this on my Taichi (actually used 1.42v vDIMM and 1.175 SoC voltage) and got up to DDR4-3466 . . . actually it was 14-14-14-28 + subtimings from DDR4-2133 default, but I digress.