At my weight, just going by the recommendations of a pressure calculator, I would be able to run about 15% lower pressure with a 700x42 compared to a 700x38. Somewhat related, I certainly noticed a difference going from 700x32 to 700x35 on one set of wheels, and making the jump from 700x38 to 700x43 on another. I run my front 700x43 @ 40psi (over 25% lower than with the 38,) and it is very plush. The lower the pressures I can run, the better, AFAIC.