having to have Windows in the background eating resources
It's a small price to pay! On a high-spec PC, it's hardly an issue anyway.
the speed of graphics updates on P96 modes - still horribly slow
I guess it must depend on your PC's spec. P96 modes are lightning fast for me.
Third is that even UAE is slow compared to the Amigalike environment I'm using now
SysSpeed thinks I have a 1Ghz 68040! :-)