I'm slow with numbers on the sides of buildings and would have to look up how to read larger numbers, not that I've ever seen any. But 11, really? It must take a long time to mentally look up X -> 10, I -> 1, long enough that another part of your brain sees the characters X and I out of their roman numeral context first and cuts off the calculation, causing you embarrassment which is not strong enough to condition for seeing roman numerals where appropriate?

I think the Super Bowl uses roman numerals and must be around 50. I wonder if the average fan, vastly less equipped than you to do any kind of mental exercise, goes around saying "Super Bowl el" since they don't know what L means in that context? I guess they must!