Rygar did a lot of research on this:
https://www.project1999.com/forums/s...53&postcount=1
Basically up to 200 wis it's 12 mana per wis (at 60) and then 1 mana per after. So, get 200 wis and then focus on +mana items (though apparently there's a cap on how much +mana you can get from items).
-Mcoy