Fresh build of xvc for Windows x64 here:
https://drive.google.com/file/d/1MOZ...ew?usp=sharing
Let me know if you would like a build for a different platform (or if you would like to use ffmpeg with xvc support instead).
For Park_Joy, 8 mbps you should probably be using around QP 27 for 720p and QP 30 for 1080p.
I would suggest -speed-mode 2 if you want the result reasonably fast, or -speed-mode 1 if you want the highest quality.
Example command line:
xvcenc.exe -input-file park_joy_420_720p50.y4m -speed-mode 2 -qp 27 -threads 16 -rec-file rec.y4m -output-file enc.xvc -verbose 1
Took around 30 minutes to encode on my laptop and gave bitrate of 7.7 mbps.