My bad you guys I found my answer on another website
In SoA-only installs, they actually receive a 2% per level MR resistance bonus every level. In theory they could cap out at 80% at level 40, but the XP cap keeps them to 38% at level 19.
With ToB installed, they receive 1% per level until level 20. At level 20, they start alternating between +5% and +1% MR each level. This leads to a theoretical cap of 84% at level 40.
Why they decided to change it from the slow, steady, imminently predictable SoA scale to the one in ToB is beyond me, but in both cases there is no 14% startout bonus. I believe Nick's already got a topic floating around here about updating this kit description.
Lesson learned for wizard slayers: don't install ToB until you hit level 20."
However with only SOA installed you can only reach level 19. That's the cap. However with ToB installed you can use potions with your wizard slayer. Otherwise you can't in SoA unless you have ToB installed. Not sure what would happen if you had SoA till level 19 and then installed ToB to get the new level up charts. Would it keep you at the old SoA amounts and end at 80% mag resist. Otherwise if you timed your installs right by my math theorically you could end at lv 40 with 104% mag resist.