On the other hand, xp per level for a girl might actually be on the low side. It's currently just 8 experience to bring a girl from level 40 to 41, and the best rare book gives 140, meaning that the girls won't be using those for quite a while. If the experience always grows at the same rate, 399 to 400 requires just 30-50 xp (high margin because it's hard to tell the growth factor for now)... Assuming the growth rate puts it at 50 to go from 399 to 400, it will cost around 11000 to get to 400 from level 1, which is just a bit over 78 of those books that give 140 experience per girl. Of course, growth might be exponential, it's hard to tell for now...