When you're talking about pinkies vs. fuzzies, two pinkies probably do not have the same nutrition that one fuzzy would (although without doing the 'math' I couldn't be absolute) simply for the fact the rodent is less developed physically.
As far as digestion goes, it's probably easier for the body to digest two pinkies over a fuzzy, but the snake will be eating much larger prey than a pinkie once it is an adult, and their stomachs are designed to digest tough 'stuff'.
I never did the two pinkie "step" and switched over successfully to mouse fuzzies (the pinkies the store had just looked so tiny), no problem. As long as the temperatures are correct for digestion, and the prey size appropriate, a healthy snake should have no trouble.