to answer your question, I took my wis to 58 and havent added another since. I'm level 46 and only have 29 con. but I have been putting a bit in Int as I raised my wis up, for damage with spells and better healing.
Each level, I have been going 1 con 1 int and 1 agi. I am raising agi so I can sleep/freeze before others; I get more xp that way than attacking...
It would seem to be VERY hard to level by going all con/wis...I only had 12 con until level 20 something..
But that's what I'd doing and its going well for me. It's your character, you do what you want.^^