Around home where I am not riding a heavily loaded bike and my steepest hills are a 7 percent grade, I ride my Nomad with gearing that is quite different than I use for touring. But touring, I want the lowest gear that I will find to be practical.
The net result is that I use a 44T chainring around home, sprocket is 16T. I set the gearing to be in a range that I found to pretty much meet my needs around home with a dérailleur bike. With these gears I never find that I wished I had higher or lower gears, I have the range that I want covered. Ratio = 2.75.
For touring, I felt that the lowest speed where I could maintain vertical and directional stability without excessive steering was about 3.5 miles per hour (5.6 km/hour). And I wanted a minimum cadence of 72, slower and my pedaling is not as smooth. With a bit of calculations based on a 26 inch wheel diameter with a Marathon Extreme of 57mm width, I figured out that I should use a 36T chainring with my 16T sprocket to give me that gearing. My highest gear is too low for shallow downhills where I usually would pedal down the hill with a low cadence and low torque, this gearing is too low for that. But if I have to lose something, I would rather lose my high gears than lose my low gears, so that is the gearing I use. Ratio = 2.25.
When it comes to the Rohloff criteria for minimum ratio, I am about 80 kg in weight. I do not recall what their rules are, but they have different minimum ratio for body weight over 100 kg.
You asked about different gearing and you listed a change in both sprocket and in chainrings. I would suggest you only change chainrings and not the rear sprocket if you wanted to run different gearing for a tour like I do than you would for normal use. It is easier to change one instead of both. When I change chainrings, if I switch from the 36 to 44 I add a second quick link and a few more chain links, or remove those extras when I switch to the 36.
Regarding your question, would you notice a difference between 40/17 (ratio = 2.353) and 38/16 (ratio 2.35), those gears are about 1 percent apart. Upshifting a Rohloff by one gear is about 13 percent. You would probably never notice the difference between those two setups when you consider how small the change is compared to the change of one gear shift.
Big tour, mountains, plains, deserts, etc., I think you might want to lower your gearing a bit but you should not fall below the Rohloff minimum ratio for your body weight. Since you have a Nomad, I assume you are talking about a heavy load. I have a slightly lower ratio (2.25) with my tour gearing than you have (2.353), but not by that much. Your first gear is between my first and second gears, but your first gear is closer to my first than to my second gear.
We both have a higher gear that Dan. But he has a higher cadence than me so I think it would make sense that he have a lower gear than me.
In the photo, the hill that I had just climbed, I got off the bike and pushed the bike up the hill. It was too steep for my gearing. But, I would rather get off and push than have a heart attack, we have to know our physical limitations. A lower gear would not have helped me there because I do not have the power to maintain speed while climbing a hill that steep with a heavy load.
Good luck with your trip planning.
