With Xtol stock, I develop HP5 exposed at EI 250 for 7:30, continuous agitation, 20C. I much prefer a 1+1 dilution, or replenished. Then it's 9:30. HP5 at ISO 400 in Xtol stock is quite lovely. It's been a while since I tried it though.
Since you are down rating the film speed develop the film at film speed or you will have wasted the effort of shooting at 200. Since XTOL gives a boost to film speed why not shoot and develop at box speed to see if decades old traditional films can stand on their own?