It depends. And you don't have to pick an exact number to add, just choose a mag percent you want to maintain and after every level add str/int to keep that percentage. Make sure you're naked though. You can also use this
http://bobtheveg.dyndns.org/SRO/Char_Build_Applet/ to keep track if you want.
There are some guides for hybrid int but it's usually just personally preference. Add more str if you want to survive better, more int if you want to deal more damage. If it was me, I would just keep the 85% going. Just remember in pvp you'll need to use heuksal skills since your nukes won't be that damaging.