I gave the "vga=..." a try. I looked into the vesafb.txt for valid vesa modes, but none of them worked.
I tried 0x313, 0x317, 0x318 and some 8bit resolutions too, but none of them worked.
I think it's not that bad so I will stay with a standard text console and leave it working... like erwos said: "open an xterm like everyone else"
I think I will do so
So thanks to all, you guys helped me a lot...