Thanks for your help - sorry just tested again and isn't working. Using the following lines it always switches to 2560x256 @ 55hz, can you help me fix it?
crt_range0 15325-16102.76, 55.50-65.00, 2.850, 7.499, 6.149, 0.064, 0.192, 1.024, 0, 0, 192, 254, 384, 508
crt_range1 16102.77-16122.77, 48.50-55.49, 3.111, 4.888, 6.665, 0.683, 0.745, 0.869, 0, 0, 256, 285, 512, 571