I'm no chemist (but I stayed at a holiday in express last night), but it would seem to me that the limit placed on a 60 which is a true 75 almost certainly is at the "top end", meaning charging to 100% is actually charging your battery to 80% and therefore would cause no degradation. The only other way to limit the charge would be to disable 20% of the battery cells in the 75 to make it a 60, which is pretty harmful for those cells, and in which case the 100% charge would mean you are charging 80% of the battery to 100% charge.