Schwalbe Marathon Supreme's are the one's I go to for the best non-skinny tire that I know of.

I think 40c (1.6") is the best compromise between speed and comfort if you have a cheaper / older bike, or are riding like actual dirt roads. In my limited experience you gain a little rolling resistance between 25c and 40c. It's there. But it's not "enormous" or anything. But when the tire gets bigger than 40c the rolling resistance (or maybe it's the weight, who knows, I just know it's slower) goes up a lot more noticeably, with a lot less gain in comfort or grip.

I don't find 2" slick useful for much, personally. 40c is all I need for comfort or even dirt roads (cyclocross is off-road, and their tires are typically 35c if I remember right?). The only bike I have 2" tires on is my mountain bike, with knobby tires.

I say for the 1.6" tires for sure.