Do Nikes run slightly small than Air Jordans?

I normally wear a size 12 but lately I have been buying sz 11 shoes and they seem to fit. Im am going to buy a pair of Nike Triax Structures 91' and I hear they run big but im not sure if I should get a sz 11 or 11.5. I have two pair of sz 11 spizikes and they fit tight but its like a perfect fit and I have a pair sz 12 VIII's and its like a perfect fit with little room. But with my SB's I have a sz 11 and they fit really tight and sz 12 foamposites fit sort of tight to. Which sz should I get? 2 hours left on ebay hurry!!!