I find that Specialized All Condition Armadillo Elites in 28mm make great light touring tires on my 1993 Trek 700. I outfitted that same bike as a gravel grinder with 40mm Schwalbe Smart Sams. Riding on pavement I was surprised to find that it really didn't make that much difference to average speed or effort. I'm still in that 15-16 mph over 50+ miles in gently rolling hills. The larger tires do make a significant difference in road buzz when the surface gets rough and roll over gravel and other less ideal surfaces more smoothly. Perhaps a 32-35mm in something like a Schwalbe Marathon would be a good compromise.