Even though, as a scientist, engineer, and academic, I generally prefer the Metric system, I really like Gear Inches, because the system is nicely calibrated to percentages of what used to be the default top gear of 52/14 = 100 gear-inches. Thus, a 50-inch gear requires half the pedal torque of a 100-incher. It's easy and very intuitive. It is also easy to relate to the old English wide-range 3-speed bikes, which were typically geared something like 50-66-88.

As for your questions regarding chainring and cog sizes, all of my road bikes have top gears in the mid-90s. For this I use a top gear cog of 13 or 14T and outer chainring of 45 to 50T. 45-42T works fine on the Peugeot with an old Shimano Titlist front derailleur.