I maintain a lower cadence than Dan (on average 90). I use 38 x 16 on my Rohloff-equipped Raven Tour.
This gives me a range of about 17" to 89" with the 26" x 50 mm tyres I use. At 90 rpm that is about 7.4 to 39 km/h, it would be about 8.3 to 44 km/h at 100 km/h.
I very rarely use the highest gear, and although the lowest has got me up anything rideable so far, I never say no to lower gears, so will probably drop the gearing when I wear out the 16T sprocket, either slightly to 38 x 17 or more substantially to 38 x 19. The 38 x 17 combination has the advantage of being compatible with my Chainglider.
On my last long loaded tour in 2011 I had a derailleur setup with 18" to 86", the highest gear wasn't really useful but I did use the next-to-highest 75" gear quite often on the flat with favourable winds and on slight downhills. Lowest gear was used a lot while climbing mountain roads and on off-road stretches.