I started in Mac because in 1992, that was the only way to have Archicad. It has remained a largely trouble-free and easily understood interface. The machines seem to last a long time and remain usable long after PC machines fizzle [anecdote]. Except that my 17" MacBookPro has fritzed its display after only two years - the only disappointment in twenty years of ownership. And I already owned a white hat.
It is true that iMacs have limitations, but represent excellent value and maximum coolness. In many offices, as they get obsolete, they are passed back to lesser demanding tasks, but will always be adequate for Archicad modeling.
The high-resolution 27" display is adequate for Archicad. You simply use a smaller plan view and sit closer. Sort of like the old cowboys versus Indians story: 
"White man make big fire and sit far away. Indian make tiny fire and sit up close."
. Macs seem to have a 'looser' approach to screen organization making better use of a single display. I find that geezer eyesight limits my ability to appreciate a panorama of displays like in the old days.
					
				
			
			
				
	Dwight Atkinson