Got three different TFT monitors around here (Samsung, Belinea, NEC) and they all work with 31 kHz 60 Hz scandoubled NTSC. Only one (Samsung 931BF) works with 50 Hz PAL, however.
If you're not fond of changing the jumper you can use the early startup screen to switch temporarily (hold both mouse buttons before powering up, wait for a bit and then hit the space bar).
btw: scandoubled PAL runs on 31.25 kHZ horizontally (15.625 kHz x 2). Standard VGA uses 31.4686 kHz, so a very picky (digital!) monitor could very well have problems with that since a digital monitor has to sync 100% onto the source signal in order to be able to digitize it.
