CPU not Performing Well in Premiere?

So I have recently made a huge upgrade to my PC, and was expecting massive improvments over my previous PC but I'm left feeling a litte underwhelmed.

I was running a 4 core i7-3770k, overclocked, and 32GB low speed DDR3 RAM, and a 780Ti and used GPU acceleration. My footage is often from my ENT camcorders - Canon XF footage at 50mbps, so fairly demanding, but my PC handled it well.  I'm running Pro CS6.

My upgraded spec is the AMD Ryzen 3900x (12 core) running at 4.1Ghz each. It should have autoboosting when under load but according to task manager it never seems to increase power. I've installed the latest Ryzen software but no difference.

I'm running 32GB DDR4 RAM at 3200Mhz, and have an 8GB RTX 2070 SUPER GPU. Up until now, I was running GPU acceleration - then I saw that CPU performance can be increased by using Mercury Software only, and right enough, my warp stabiliser analysed 270 frames in a clip in around 100 seconds which is around 50% faster than before. But still, I'm disappointed in the speeds to complete these tasks.

Not only that, my CPU is at around 8% during the frame analysis for warp stabiliser, and around 50% usage when rendering with Media Encoder. Rendering times have definitely improved from my old PC, but again, not to the extent I would have expected. Can someone help me out because I'm sure I should be getting much better performance here? Thank you.