OBS via OBS_OpenVR_InputPlugin_v1.5 captures directly from the mirror surface, so if you have SteamVR oversampling at 3000x3000 per eye that's what you get, and can pan/crop/zoom yourself silly in editing.
SteamVR only does half fps, though, so you'll only get 60fps with the HMD at 120hz. AHFilm with "use recorded views" gets 60, is also capturable in OBS, but is sometimes not quite what you saw.
If Quest drivers capture the full frame at 60fps I'd look for an OBS plugin to tap into it.