There's some interference coming from me running Emacs/Magit on WSL1, and corporate nuking my Windows Defender exclusions lists, meaning "real time protection" is slowing every file write down. Still for small to medium repos it's wonderful; for that one large at work, it's... pretty much setting my tea breaks.
Currently the most annoying mysterious issue is that some commands (usually pulling or rebasing, sometimes committing too) reach the point of Magit echoing "git finished", and then... whole Emacs remains frozen for 30-120 seconds. I haven't traced that tone to source yet.
`M-x toggle-debug-on-quit` and `C-g` during the freezing will probably help here, though I would guess the problem is highlighting since that tends to take a lot of time on big diffs.
In my experience this brings emacs to a crawl.