I just noticed something pretty cool! now my laptop also works on 50hz after adding a custom resolution in the Nvidia Control Panel (probably works for Ati and Nvidia cards) or any graphics card that can handle custom resolutions and refresh rates well. my laptop normally doesnt support 50hz only 60 and now its also supersmooth in WinUAE!
To be on the safe side i left the "Timing" option on "Automatic"