Faster than I thought… Fixed my broken X server pretty quickly, and by the way learning how to boot up OpenSolaris into maintaineance / single-user mode (as this unfortunately is not there as a default recovery option in the grub configuration but rather easy to do nevertheless). Using the xorg.conf I copied off my Xubuntu system, now my external TFT finally works at 1280×1024 / 75 Hz, took some time