I came across this thread as I hesitate between 1.75 and 2.00" tires.

Evidence suggests that wider tires are a better option for touring, because (1) they reduce rolling resistance, and (2) they contribute to a more comfortable ride. So it'll be 2.00" (same as now).

(1) and (2) are in opposition - the reduced RR assumes identical pressure; whereas more comfort would be the result of a lower pressure allowing the tire to absorb road imperfections.

Schwalbe's post explains that competitive cyclists favor relatively narrow tires because they accelerate faster. Not an issue for tourers, but critical for competitors.