Hi all, finally I found some time to do tests.
Firstly, I tried two boards built end 2016: C41 with Samsung 4GB and C45 reworked to IntelligentMemory 4GB. I tried them both with different main boards (M28 resp. M16, both V5.1.3 built 20170119).
They seemed to boot a little more stable, but did either hang in Kernel or even after Starting Kernel... Once I did even see the ### RESET ### notice.
Sometimes they did boot up to login: but there were "Illegal Instruction" and "Segfault" reports in the boot log (maybe from udevd because some kernel modules were missing). I could log in and type a handful of commands, but then the kernel got stuck.
Next I tried the same SD card with one randomly picked new CPU board: 20180502 C24. I also used the M16 main board.
And the result is a stable working 4GB system! Equally to what I am used to from the 2GB CPUs. And this with 1.5GHz enabled.
I haven't run memtester or run the temperature to the maximum. Or other high-load tests, but setting up USB and apt-get upgrade did work fine and continue to run for at least 2 hours now.
Apt-get installing 400 more packages also went well, which is a load comparable to compile something.
There was one stuck situation, when the battery became discharged below 3.2V (the charger function is broken on M16). But replacing the battery with a charged one made it work again. This might have something to do with my M16 setup - it does not use the Pyra battery but a tiny GTA04 battery connected through quite weak cables. This makes power supply a more critical thing than a real Pyra will have.
So I think that both factors, having done a hardware redesign and Tony's new patches, have improved this setup significantly.
BR, Nikolaus