It very much depended on the amount of graphics scrolled as you said,shand, but there were a number of demos on the ST which utilised full-screen scrolling (i.e. without any borders, and four layers)
And some of the Thallion games were perfect, even though sideways scrolling was never going to be easy. The worst case ever was Giana Sisters, that could EASILY have been done with layers.
The quality demo guys on the ST , like The Care Bears and The Union, ripped more out of a bare 68000 setup than most could ever do. But not all, before anyone starts bleating!
The stuff they did could never be emulated. I remember the code to make full screen graphics, and it was the most intricate design you could imagine. If anyone remembers seeing sprites in the border of a C64 game then it was similar, but only in idea.