Best practices for multiple large header files?

[Supreeeme]

I have several (5-10+) ~6000 line headers I want to generate bindings for. (These headers have a lot of the same types but I post-process the bindings from bindgen to deduplicate them.) My question is what is the best practice to efficiently generate bindings for these files? Obviously I can stick them all in one bindgen call, but that seems to really slow down as I add headers. My second thought was to split up the bindgen invocations and run them in parallel, but with fewer files this seems slower than just doing it all in one call.

Is there some kind of best number of lines/files where it makes sense to split invocations across threads? Or is bindgen already multi threaded and this is pointless?