I haven't done sensitometry on APX-25 yet, but expect it to hold its speed well (I find slow film generally does), and expect to lose some contrast (so develop longer than fresh film).
With only 5 rolls, you would not likely want to waste any on tests. I would try to sneak in a step wedge on a tail of one roll, but that's just me. I keep thinking about a simple test that anybody could do anytime and interpret it easily: From the first roll of film you shoot, take two shots of the same scene with 2 stops of exposure difference between them. That's the test. They could be a shot you want to bracket anyway. The rest of the film you just shoot normally.
When developed, the two bracketed shots should differ by about 1 stop of density. So a test strip would reveal that one of the pair takes twice the time to get the same appearance as the other. That would be because you developed to about an 0.50 average gradient, which is a fairly good aim to develop film.
