I remember when I first got OS4 back in 2004. I'd had the A1 for about a year and was using a 14" Acer monitor I'd borrowed from my brother. Linux had restricted me to a max of 800x600 so when I got play with P96 I decided to try and push out the max resolution of 2048x1536 just for fun. Amazingly it worked, it was as flickery as hell and totally unusable due to the small size of everything on that tiny 14" screen.
Under AOS that simply depends on the drivers. AOS3.x supports Workbenches up to 16384x16384 pixels in size (perhaps 2.x as well). Under Linux it may simply have been a driver issue, where the desktop was restricted to what the driver could display.