Well, 50Hz is must if you are watching PAL material or you will end up in the jerky playback when 25fps is tried to sync to 60Hz (wich is not possible).
You are right, sync is not possible. But the graphic card can make a pulldown like correction, I assume? NTSC users watch 24 fps movies corrected like that (3:2 Telecine pulldown) every day. It can´t be sooo bad or jerky. I activated "pulldown detection" Avivo CCC (dunno if it is important, but recommended)
Pal dvd does not play jerky neither does 1080i/50. It does not disturb me. I tested sveral times forcing 50 Hz and e.g. scrolling text was not fluider (set it back to 60 because overscan correction is otherwise nit possible).
Believe me the 3:2 pulldown is very visible (NA people has just looked at it for all their lives and have got to used to it). Also the 60Hz doesn't give any less flickering screen with todays LCD / Plasma technology as there isn't similar on/off flickering happening as there is with CRT technology. Plasma & LCD are always keeping the pixels active, so they woulnd't have any flickering even if they would be driven with 1hz refresh rate (of cource all the motion would be very jerky).
ps. I'm not forcing you to use 50Hz, but it's better
Netherlands