I currently use https://github.com/philj56/tofi because it loads noticeably faster, it seems the secret to how it does this is by manually loading a font file, rather than having it automatically selected or selected through css, it would be nice to manually load a font file with wofi.
I'm not sure manually loading a font will fix wofi's performance issues. These are well known and well documented in the bug tracker and wofi is sort of hamstringed by the fact that GTK and more specifically certain GTK widgets with less than optimal performance characteristics were chosen during development. There is likely substantial refactoring and architectural changes needed to match the performance of tofi. At one point in time fixing these architectural problems was on my todo list with a from scratch rewrite, a sort of wofi v2 if you will but that project has long since stalled