Andre,
I developed my first K400 / Perceptol 1+2 roll.
They work great together!
Grain is very very sharp, but smaller and tighter than with Rodinal. Very photographic.
Though it's not the best film for pushing, K400 is fast IMO; it reaches 400 in MQ developers, and there's very good shadow detail at 320 in Perceptol 1+2.
My first test at 200 was clearly overexposed: so much that I didn't bother to try 250, and I went directly to 320. Much better, At 200 nearly nothing is really black (b+f).
It's not inside your asked 400-500 range, but 320 is very close... From my initial EI200 use, I was able to work at 320 with my 28mm in f/8 instead of f/5.6 1/2: great.
Have a nice day.