I have a bunch of 120 rolls of Rollei R3 and I had a hell of a time finding an EI/developer combination I was happy with.
After a lot of disappointing results shooting from EI 160 to 400 and using D-76, Rodinal and HC-110 at various dilutions I started digging for clues on the web.
I ended up finding some posts on other forums by the owner of Fotohuis, Robert Vonk (?), who is a Rollei dealer and has done extensive testing of R3. His findings suggested that R3 looks much better at the low end of the EI range and that it’s pretty disappointing at higher speeds and with general-purpose developers. This agreed with my results so I started searching for more posts from Mr. Vonk.
In a post from a couple of years later, after R3 had been discontinued, he stated that the best results would be from Rollei RLS developer but that Ilford Perceptol 1:1 would be a good substitute.
Since Perceptol is cheap and readily available I tried it at EI 100 and EI 50, both in Perceptol 1:1 and I was very happy with the results.
Of course, roll film isn’t sheet film and there are lots of variables but this was my experience with R3. Hope it’s helpful.