I hate smithing with a passion.

Thinking of making a light armor dual wield.

Wondering what the max armor rating with Nightingale Armor, 100 L. Armor skill and all perks equals?

I will not smith it or enchant it (I have a mod that makes it just armor w/no enchants on it) with light armor bonuses.

Anyone know?

It can be calculated. For any armor piece worn you get hidden 25 armor rating (100 for 4 slots). You also get 25 bonus to armor rating if wearing full set of Nightingale Armor. Then sum base armor rating of each piece 34+15+10+10=69 and multiply by skill factor which is by default 1.4 when at 100 skill, then multiply by 2 from agile defender, then by 1.25 from custom fit, then by 1.25 from matching set perk and what we get is:
100+25+69*1.4*2*1.25*1.25=426.875 armor rating and damage reduction is 426.875*0.12=51.225%. That is what math says.

use the console command player.getav damageresist I think that should do it