Input is single track AVCHD HD1080 60 fps progressive, 28 Mb/sec, 1 minute, unedited file (from Canon G40). (Resample turned off, of course.) The new Magix AVC CODEC was used.
Fury x graphics card didn't matter, since it's AMD and there's no VCE support. Memory and SSD probably don't matter either, but 16GB (2x8GB) and 500GB M.2.
Render time is 47 seconds (0.78 realtime). At worst case (1 processing thread and 1 slice), it was 50 seconds. Processing threads seems to be ignored, but slices made a little difference. CPU was about 80% busy.
With, or without, GPU selected in Preferences, the time is the same.
Comparison to Nvidia NVENC
Same file, but PC is my old one: AMD 8350 CPU (4 core, 8 threads) with Nvidia 750ti (2GB).
WITHOUT GPU selected in Preferences: Quality: 41 (0.68 realtime); Performance: 38 (0.63 realtime).
WITH GPU: 56 seconds (0.93 realtime).
Comparison to AMD 8350 CPU only
124 seconds (2.07 realtime)
So you can spend $2,500 on a new Threadripper PC, or $125 on an old Nvidia card on Ebay, and upgrade to Vegas Pro 15, and render 20% faster than the Threadripper.
Waiting for AMD VCE support!