I'm working on a project and the Product Owner has to decide *if* and *how many* new game-features implement in a SmartPhone app.
Those game-features have the goal of keep the user more active inside the app. Currently those features were explained by the Product Owner in a rough way, not detailed, but in a more generic way.

We planned a session to analyse generically every feature, splitting them in **macro areas** to develop (Drupal, Frontend, Middleware, ...), to estimate them, not with points, but with t-shirt sizes and the goal was to understand effort, risks, reusability of common components. At the end this estimation should output sort of a charts of features, from the most efficient to the last.

With efficiency we should consider users interest (coming from a survey) and estimation sizes.
But, how could you precisely analyse t-shirt sizes like XS, S, M, L, XL?
Would you map them with 1, 2, 3, 4, 5 and sum them? Or just check with gut feeling which one could be the most efficient to implement, just having a look at the sizes?