Ahh...most responders do not fully understand the question I am asking...
If my tm guy only has 0% potency, even with tenacity down it will be resisted half the time because of the level split.
Resist chance = tenacity-potency+levelsplit*10. ...... I think, with a minimum resist chance of 15%... And a max of 85%.
If tenacity down reduces tendacity to 15 then my magic number is 50%potency(more then that is unnessary). If tenacity is reduced to 0, then I only need 35% to only be resisted 15% of the time. I think the case is the later.