EDIT: Sorry, I wasn’t quite watching what I was doing, and I overwrote my OP.
Can you get, and does Shotcut support some sort of encoding card? I suppose that’s perhaps where the GFX cards come in to play with the experimental acceleration?
Failing that, I suppose I can drop an i5 1150-socket CPU in to this machine which will be about the same price and the simplest overall.
There is alot more to consider about the topic of encoding performance… Your CPU is probably the most important, then hard drive speeds, then RAM. Regardless of all these hardware pieces, the quality of your encoding is always going to be slower and slower. The higher the quality, the slower the encoding is, and takes. If you want faster encoding, reduce the quality profile. For example, ultrafast in AVC/HEVC is, well, ULTRA fast, but you accept the fact that the shortcuts it takes to encode faster leaves you with a lower quality video. There are many topics, and sites arguing/debating/suggesting how to encode with a balance of speed and quality. I personally do not mind that my encoding time is slower in order to increase the quality of the output.