very nice and pretty great spec too,think your right with having gone as far as you can without capacity change/new internals
what are you looking for from it- track focused,fast road,more straight line,better handling or just an itch for something different?
id be very tempted to just enjoy as is,cant see m3 or evo being much faster unless you get a mightily tweaked one,dax would be a different league but a bit lairy impractical for the road