The 400 is reportedly smooth and similar in power to the 500 with less weight to throw a around.
I did get a chance to look one over, but didn't take it for a spin before it sold.
The 500 was a bit of an odd beast IMHO. It seemed to exist because the 250 was marginal for faster roads.
I looked one over & did take a short ride, but eschewed it for a used Burgman 650, not because it was a bad bike, but because the burger is really quite nice.