RE: Do not load Firmware 5.0.0!
I haven't loaded the 5.0.0 stable version yet, but I've been running the 5.0.0 RC for about a month now, or however long ago they released that. For those not aware, RC (release candidate) is after beta testing, but before release of the stable version.
I've not had any issues except the higher speeds mean that certain thin overhangs that worked fine before don't work as well, and certain infill options (especially grid) can cause nozzle to make very obvious noises as it runs into them when it did not previously. But these seem to just be slight growing pains to learn as a tradeoff to the new speed.
RE: Do not load Firmware 5.0.0!
Revert from Firmware 5.0.0 to 4.7.2 on MK4 by loading the older firmware onto a USB stick. Restart MK4, initiate the firmware update process, and select the 4.7.2 version from the USB stick for downgrade.