Hi ahofle,
It seems that it only works if we replace the whole monitor definition, by adding these lines:
monitor_specs0 15250-18000, 40-80, 2.187, 4.688, 6.719, 0.190, 0.191, 1.018, 0, 0, 288, 448
monitor_specs1 18001-19000, 40-80, 2.187, 4.688, 6.719, 0.140, 0.191, 0.950, 0, 0, 320, 448
monitor_specs2 20001-29000, 40-80, 2.910, 3.000, 4.440, 0.451, 0.164, 1.048, 0, 0, 384, 576
monitor_specs3 29001-32000, 40-80, 0.636, 3.813, 1.906, 0.318, 0.064, 1.048, 0, 0, 576, 768
monitor_specs4 32001-34000, 40-80, 0.636, 3.813, 1.906, 0.020, 0.106, 0.607, 0, 0, 576, 768
monitor_specs5 34001-38000, 40-80, 1.000, 3.200, 2.200, 0.020, 0.106, 0.607, 0, 0, 600, 768
I'll need to fix this, anyway try this because I'm getting 320 lines resolutions now with these settings.