First, the only thing you care about for gearing calculations is the diameter or circumference, not the width.

Tires are random as heck when it comes to their labeled size vs their true size. Profiles vary too. I have Schwalbe Kojaks that are labeled 700x35. They barely measure 32mm wide, but are a true 35mm tall. I have some Specialized tires that are the opposite. They are labeled as 700x45 and they measure a full true 45mm wide, but are only 40mm tall.

Personally, I can feel a big difference with every significant increase or decrease in size. If the bike is just for putting/cruising around, bigger is better IMO. Lots more comfort, especially on rough surfaces. If you are going to be riding quick, and care about weight, keep them as small as your confort level can tolerate.

If you look around, you can find large volume tires that are pretty light too.