I shoot HP5 at 200 iso (many folks here do as well) for better shadow detail. But I develop in Rodinal, which isn't a fantastic shadow-rendering developer.
I'd just try cutting your development time by 30% or so. You could cut off a third of the roll and try that, then fine-tune for the rest.
My advice though - judge development by your final output. If you scan, dry the test strip and see how it scans; if you print, find the max-black print time using the developed leader in the enlarger (that's the max black the film can produce in a print) and use that exposure time for a test print. I shoot for negs that will make an acceptable print with a 2.5 filter at the max black time. I've been doing this for some time, but I'd rather judge a neg by its final use then just eyeballing it.
One other note on devleopment testing - you can test by putting even a couple frames worth in the reel - but agitation will be massively more effective that way, so it's tough to really dial in your time. If you agitate for 5 seconds every 60, for instance, when there' a tiny piece of film in the reel, just give the tank a gentle tilt each minute.