The highest I reached was LV 46:

http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Main=28168&Number=445213#Post445213

I don't think it's possible to get to even LV 50 even by using the respawning enemies as grinding material. I may have reached LV 47 or 8 if I had maxed out wisdom.

Let's Play Divine Divinity - The Damned One's Tale - Chapter II.