Efke 25 at 100?
As far as I understand the general rule is 2 minutes per stop so you would go from 9 to 13 minutes.
You should get Rodial, it's super cheap and super awesome.
I have HC-110 but I don't like it and haven't pushed with it but I know it's possible and would go with that one with the options you have.
However I would qualify this whole post by saying I've only been developing for a year. I've successfully developed a lot of things that people said couldn't be done like film from 1947 that I shot and then developed, however, I'm no expert, just an avid enthusiast of film. I've been shooting for 18 years though... Just recently (the last year) got to the developing side.
If you live in the states, I'll trade you the Rodinal for my bottle of HC-110 if you don't like it.... Haha
Hope that helps in some way.
Mamiya: 7 II, RZ67 Pro II / Canon: 1V, AE-1, 5DmkII / Kodak: No 1 Pocket Autographic, No 1A Pocket Autographic | Sent w/ iPhone using Tapatalk