Thanks Oshyan,
And no, I didn't had anything else running while rendering.
I have 8GB RAM so other running apps can benefit from the other GB's left over.
You say it is not *at* the 4GB limit, but TG2 is 32-bit and theoritically can use 4GB in a 64-bit OS, but is it really capable of?
I did another overnight render with reduced crop-size and that again had problems. Got 6 traceray errors and 3 of the 4 threads were dead without further warning.
Also the GI-prepass had 2 completely black (bucket)holes. It was still rendering, but with 1 core and it wasn't at 20% even, so that would take an eternity to finish. So I aborted it.
I can lower AA and choose another pixel-filter, but honestly I really like the settings now as they are, however they are quite demanding.
Martin