Regarding performance, it varies between minor to negligible. If you are already running at very high FPS the cut would be more pronounced, but that is just math, when introducing extra microseconds every frame.
Regarding XP11 vs XP12. XP12 broke the previous multi-threaded uploader. The build in v2.0.0 of the Islander is a slightly older version of the new version than what we have in the SR2Xs (just due to how we got these updates out). I've found with Mac the latest builds of the system (as seen in the SR v2.0.1) have removed the issues for me, and we'll be rolling this into v2.0.1 of the Islanders. Something minor of note, we no longer do testing on Intel Macs ourselves (we've all moved on to M1+ based systems), so behavior there is less predictable there.