I can't tell you much about StaxRip, as I don't use it.
But I can tell you if you want the best ratio between speed, filesize and visual quality, there are not many alternatives to x.264/x.265 encoders.
And don't get your hopes up too high with the upcoming Ryzen 4000 series.
HEVC encoding takes time, especially with 4k content IF you want to have a decent quality.
I have two rigs running 24/7 with an AMD Ryzen 9 3900 and a Ryzen 9 3950. With 4k material I usually end up somewhere between 1-4FPS (custom "slower" preset) for HEVC encoding, depending on source material and filter settings. 1080p somewhere between 5-15 FPS (again, custom "slower" preset).
x.264/AVC is a different story. 1080p at x.264's "very slow" preset ends up with 50FPS and beyond.
(You see there is a huge difference between HEVC and AVC when it comes to encoding speed.)
Even if Ryzen 4000 would be like 50% faster than 3000 Series (which is a very very optimistic guess) you'll still end up with speeds somewhere between 2-6 FPS.
I'm just talking about consumer CPUs. Threadripper may be a total different story. But you'll have to spend a lot of money for CPU, board and RAM...
Long story short: IF you want a decent quality you have to be patient with your encodes.