So i just bought VP18Edit and configured just like VP17Edit. Having a 33,5 GB HEVC file (~ 65 Mbits of 1 hour and 10 minutes) generated by OBS on a RTX2080Ti i proceeded with encoding (AVC for YouTube: 1080p60, 12 Mbit, 192 Kbit) in both last versions.
Unfortunately not much difference on my system:
VP17 - CPU hovered around 25% (max 30%) - both versions had set 6 cpu threads in options and GPU was max 45%. Finished the rendering in 34 minutes.
VP18 - CPU almost the same and GPU was definately much lowered used.. maybe 35% iirc. Finished in..37 minutes and almost all the time told me it was using 2 gb of memory.
later edit: i see that VP18 has two pass for NVENC now.. will test it soon.
second edit for fr0sty: Ryzen 3900X + NZXT X62 280mm, 32 gb ram, 1 gb ssd, rtx2080ti.