I currently use OS 3.9 on my WinUAE set up. It`s superb with the p96 setup i have...
But i use a `customised` OS3.1 setup on my 040 Amiga... i found that most of the features of os3.9 can be a drag to the overall performance...and that most can be replaced with third party software...
as for 0s3.5 , why? :-D