Quote Originally Posted by StigHagen View Post
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.
With all due respect to your own findings about your chosen developers and Ilford HP5+, I must say that suggesting to change developer to fix an exposure mistake may not be ideal, because other factors come into play when you do. The OP already has one variable that is way out of bounds from his normal work flow; if you add another variable to the mix you're totally in the unknown.

If you want to try a new developer, my suggestion is to do so when all other variables are under control.

Also, many factors play into what you find as an Exposure Index for your chosen film. Metering technique, lighting conditions, light meter accuracy, film developer, film developing technique, lens contrast, lens shutter accuracy, water quality, bellows draw calculations, etc.
Using HP5+ I find that I get the best results with full shadow detail at EI 400 in normal contrast lighting, using modern high contrast lenses, and replenished Xtol developer. More than a stop different from your 180, and we are both correct. I know those who use it at EI 800 as 'normal' too, and Dr5 reversal process has EI 1,000 as 'normal' for HP5+. Go figure.