I made wanna be sweetpotato fries on my first and only attempt at eating them...cut em up, added loads of spices(mainly chili...nice and hot!!) and put just a tad of olive oil...oven for like 20 minutes and oh boy that was good!
Life is what you make of it, not what it makes you...TAKE CHARGE!
Use common sense when buying the sweet potato...if it looks smaller than the rest, it's small. If it looks average, it's medium. If it's one of the larger ones, it's large. If you see one and say, damn that's a big potato, I'd say it's extra large.
oh, and no, not all potato's have the same nutritional value. Even two medium ones will have slightly different values. But basically they are close, so they group them into small, medium, large.........