After a night of test installations today I managed to install a stable version of 9.1+ onto a 7200 with Sonnet G3/400/1MB L2/224MB RAM, ATI Rage, 1GB Harddisk and a TEAC CD burner with patched Apple CD/DVD driver (also a generic Fast Ethernet card with Realtek chip and the known mediocre driver). Before purchasing the upgrade, the machine worked with a 9.2.2 installation (OS 9 helper 1.0.1), slowly but reliable. The ATI driver support was a _big_ improvement compared to 8.1.
After installing the G3 upgrade it turned out there is no way to get the existing Sonnet driver cooperate with a 9.2.x-System. To apply the System update to a 9.1 installation disables the Sonnet driver. The few posts providing hints how to solve this problem contain no workaround that really works (I doubt one succeeded). Sonnet does not distribute driver Software for the Crescendo 7200 G3/G4 cards compatible to System software newer than 9.1. Please keep in mind, that the System 9.1 with the Sonnet driver patch is not bootable with extensions disabled
So be sure to have another boot drive available when tuning the system.
In the end I did a clean install of 9.1 (without the upgrade card), installed the
Crescendo/7200 Processor Upgrade Software v. 1.1 and added/replaced any working extension/control panel in the system folder by later versions from 9.2.1 or 9.2.2 respectively. In the result the machine boots a lot faster than before and is very nice to work with (1024 x 768 in True Colour). This computer still is the working horse in a little shop. The owner uses some old programmes to make invoices with a beautiful layout, nothing else. If it was not a PPC, it would be a good candidate for the next endurance challenge, as the machine is on duty since it left the factory