I believe borates stay where they are, much like CYA. I have more than 50 ppm, prolly around 60-65 (I had overestimated my pool volume). My water looks and feels great.
I don't think it's harmful to have borates over 50, just doesn't offer any add'l benefits. Other folks here may have different info. [edit: the pH does tend to go high and I have to add acid a couple of times a week. Possibly I wouldn't have to deal with that if my borates were a bit lower.]