I wanted to do the tests anyway, to understand a little more what's happening
There are a lot of ways to do the tests. This way is based on sound principles and is pretty easy to do and to understand: Do a Zone I one exposure test at various ISO/ASA settings and keep good notes, and process the film. Place the processed and dry negatives of zone I over your meter. The one that drops exposure by 1/3 stop over unexposed film base equals 0.1 log d and that is the one to base the speed on. Next, using the speed you had just determined, you can shoot a zone VIII target. Do that on three rolls. Process the first roll for your usual time. Place the zone VIII negative in the enlarger so you can also see the film edge. Do a test print so the film edge is just black. Now the Zone VIII should be just off-white, very slightly gray. If it is totally white, then process the next roll for 25% time less and repeat the test. If the Zone VIII is a darker gray, then increase development 25%.