Please help testing upcoming openMSX release!

Okay, gonna play a bit with the RC
If I'm correct, it's a build including up to commit 6256d6c.

I notice no mention of the OPENMSX_HOME env var in release notes or docs.

Probably the Setup Guide? There's 5. User Preferences there, maybe split that up in 2 subsections:
5. Preferences
5.1 Environment Variables
5.2 Settings

Btw, wouldn't it be more appropriate to have 4. Palcom Laserdiscs as a subsection of 2. Machines and Extensions? (Perhaps 8. Writing Hardware Descriptions as well.)

I see the RC has been updated (again) (upd: no it hasn't :))

Since it exists, I would document it. Why opt for obscurity? Just put a warning then / explain their 'hacky nature' / 'use only when you know what you're doing' / 'feature may be removed in future update' etc.

Besides, one actually reading (consulting) the (official) manual is probably an 'educated' user already..

(And personally, I was surprised to find out about some undocumented env. var by chance..)

Can't help to notice that even on the latest builds delay in flashwriting and writing to soundchips are not being emulated. FMPAK works fine on the emulated turboR but the real thing really needs some extra waitstates.

Are you aware of this emulation difference?

Thats the one indeed. + to add that when writing to the megaflashrom the delay is not emulated so i can write at ligjtspeed to the flashrom.