I have tested HP5+ in Xtol and ABC Pyro. It is really an 180 ISO film in Xtol and 125 ISO in ABC Pyro to get the best out of it. Yes in ABC pyro it is almost 2 stops slower than it states. So 4 stops I dont think would do any harm, probably it will even look better than if it was rated as 400 ISO. ABC Pyro is grainy though, but how big prints do you want? Many love using Pyrocat HD, it builds a lot of contrast with stain and has finer grains. Maybe this is the right moment to try it? Test with some test rolls first. Maybe you will stick with Pyro forever.