50Hz hmmm.
On my PC, I see flicker at 85Hz refresh rate on plain white. This is enough to cause me eye strain. I run my PC monitor at 100Hz.
I do have one 1989 VGA 14" VGA monitor that afaik is single sync (it has black border arround the outside of the screen so the picture doesn't fill it). at 60Hz I don't see flicker, strange.
Could this cause me problems with scandoubled Amigas on PC monitors.
Single sync doesn't have much to do with the monitor having a black border; that's just down to it being an old, "goldfish bowl" type tube :-) Whether you see flicker or not is down to the phosphors used in the monitor. They glow for a certain length of time as the beam passes over them. The problem is that you can't change their "decay rate", so if you want a monitor capable of doing 120Hz, it's gonna look flickery at 60Hz cos if it didn't, every 2nd pass of the beam would be redundant (if that makes sense :-? ) So, a monitor from 1989 will only be made for 60Hz or so, and so will have much slower decaying phosphors than your new monitor, hence it doesn't flicker.
So, finally, it's nothing really to do with the differences between an Amiga and a PC's video output...