Playing this right now. After browsing the Thread for a bit, I guess you cannot reach Breast Size 5 on any other path than the Bimbo-Path?
I did the experimental stuff and then two enlargements, going to size 3. Then the Dream to become a Bimbo, resulting in 4 and currently at the Farm getting 5.
Like, I am all for Bimbos, but Kira becomes a little bit too stupid and tiresome for my taste. Especially because there is so much dialogue in this game, I really feel like my own brain is slowly dying while having to read things as "like", "meanie" or "preggers" around 100 times.