I have a different approach.

I reckon I can do without very high gears, but a very low gear is always useful on a bike used for touring with a load in hilly areas. So I specified the lowest permitted available option (38x17) on my Raven Tour when I bought it in 2012.

After Rohloff changed their lowest permitted input ratios, and as I got older, I changed the sprocket to 21T. This gives a lowest gear of 12.8 inches and a highest gear of 67 inches. The input ratio is just under the minimum now specified by Rohloff, but I don't think I will be putting out lots of power when I use the low gears. A bonus with 38x21 is that I can still have a ChainGlider, I simply changed the Rohloff-specific rear part for the standard rear part that I use on my Nexus Premium equipped bikes.

So speeds of 5.5 km/h to 29 km/h at a cadence of 90 rpm. That low gear is only really useful on steep inclines when I am tired, for example at the end of a long day in the saddle. In that scenario, my cadence also tends to drop so I can go as slow as 4 km/h, which is about my limit for keeping balance on a loaded bike on a reasonably good road surface.

At the other end of the scale, highest gear is rarely necessary. On a long ride I won't normally be going at 29 km/h. With a loaded bike on fairly flat terrain I reckon an average speed of 18-22 km/h is reasonable at my age (70). This corrresponds to gears 10, 11 and 12 on the Rohloff hub, where gear 11 (direct drive) is the most efficient in the range.
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For my utility bikes I just choose the lowest gear combination that still allows a ChainGlider. This is 38x22.

With a Nexus 8 Premium, that gives a range of 23 inches to 71 inches, so with my preferred cadence of 90 rpm that translates to 10 to 31 km/h. And a narrower range of 30 to 68 inches on my old Sturmey 5 speed.

These more limited gear ranges are still OK for the trips I do with these utility bikes, except when I am towing a loaded trailer. I recently did 3 trips to the local recycling centre carrying about 80 kg of rubble each time. As the centre is up a moderately steep hill I had to push harder than I would have liked.

The short-term solution is to fit the steel seatpost and towhook off my "new" utility bike to my Rohloff-equipped Raven Tour, the longer term solution will be an electrically assisted bike.

I have already sourced an old steel-frame ladies' style mountain bike that should be suitable for a conversion, but haven't yet decided whether I will start with a simple front hub motor conversion or go straight to a mid-motor, which is a bit more complicated and puts more stress on the hub gear. Ladies style in case I have trouble getting my leg over a diamond frame as I get older.   

My other limitation is heart rate.  If I pedal too hard, heart rate shoots up to levels I do not like to see it.  I do not have heart problems and I want to keep it that way.  So, I use a heart rate monitor to tell me when to stop, get off the bike, and walk it up the hill.

I never thought about all that when making my choice, 

I am an engineer (retired), so I of course I tried to use a scientific approach.  I tried to pedal up a steep hill near my home several times to see how slow I could go and still feel comfortable that I am stable and not oversteering and overcorrecting.  That was how I came to the 3.5 mph criteria and the cadence of 72.  If I tried a cadence closer to 60, I noticed the slow down and speed up pattern as I pedaled, thus I set my target for hill climbing at a cadence of 72 that felt smoother.

I have pedaled up hills on my Nomad Mk II in first gear with a cadence of 60, thus about 2.9 mph, but those were on good days without wind, minimal traffic on the road so I felt more comfortable being further from the edge, etc.

I had a bike fit years ago when I bought my RST.  Best thing I ever did as it fits me like a  glove.  It's now converted to an E and still going strong.
Kevin Sayles looked me over a few years later and built me a superb Woodrup Chimera.

Thanks Mickeg, interesting ..

Effectively, for me 36x16, the most important gear is the  first, i can climb almost  any hill..

But, my next Surly chainring  have 35 teeths, i got a good price for it,  I don’ t know if i have to keep my sprocket in 16 teeths or maybe 17 ! but i'm afraid to ́lost my first short gear..

For information, 36x16  transmission,  above 33km/h you can no longer pedal, sometimes it’s frustrating

My cadence has varied over time.  For the past few years, it usually is in the range of 66 when I am doing a multi-hour ride.  If I am working to get up a hill in a low gear, I try to raise it up to 72.  But if I have been in the saddle for most of the day already, it might dip down to 60.

I mentioned I use 36T/16T (ratio of 2.25) for touring.  But for riding around near home with an unladen bike, I put a 44T chainring one the bike, add four more chain links for a ratio of 2.75.  For riding near home, I never need a gear higher than 14 with that higher range of gears. 

But for touring, I value that low gear, so I can live with the loss of the higher gear that I would otherwise use on shallow downhills.

When I built up my Nomad, I calculated that if I wanted to use the stock 16T sprocket, pedal at a cadence of 72, and have a speed of 3.5 miles per hour, that I wanted a 36T sprocket.  I find that I can't get below 3 mph without oversteering to try to maintain stability, both directional and vertical.  And a cadence of 72 feels smoother than anything slower.  My point is I did some calculations to figure out that I wanted the 36T, I did not pick it at random.

And the 44T, that range of gears pretty much mirrors my range of gears that I think are ideal for riding near home on my other bikes.