We took delivery of our 'Raven Vitesse' late May, since when we have travelled 1450 miles.
Ours is in Small size, all up weight under 125 Kg. Used on tiny country lanes wherever possible, with plenty of broken tarmac and sunken badly filled services trenches. We have hit big feeling bumps at more than 30mph. No wheel trouble at all. We have the Mavic X618 ceramic (lightweight) rims with the 1.5" tyres and tandem carbon fork. The leaflet that came with the rims seemed to imply that a big bump might cause cracking in the coating (not detrimental), but we have seen no sign of that happening, so I suppose the spokes are supporting the rim adequately.
The Rohloff manual compares their 32 spoke wheels with 48 spoke dished wheels, and the spoke tension is allegedly less on the Rohloff. I'm inclined to believe them.
Our machine is geared 44 x 16, 71 inches or so in 11th gear. We cruise at 17 to 20mph in this gear. I was wondering about getting the 15 tooth sprocket (76 inches in 11th, or half a gear up on what we have now), but probably won't. Not before we wear the original out, anyway.
I haven't ridden a Rohloff solo, but suspect that on a tandem the shifter might feel a bit 'woolier' owing to the increased cable lengths.
We are delighted with the Vitesse and the Rohloff Hub. The next bikes we buy will be Rohloff solo's (the train companies won't take the tandem on anything other than the main line).
On solo's we would average 12-13 mph (the wife's speed). On my own on a solo I could average about 15mph. On the Vitesse we average up to 18mph over 20 miles or so, 16-17 over anything up to 80 miles and when we tried the 100 we still averaged 15.5. This is across east anglia, which has undulations but no mountains. So yes, a tandem is definately quicker than a solo.