If you use characters like Č Š Ž etc., the encoding switches from 7-bit to 16-bit, which means 70. :P (In fact, it's 67 due to the UDH.)
When I send long SMS messages (longer than, let's say, 5-6 "part messages"), I send it as MMS. And no matter how long the text, it's always only one MMS. And...