Tandem Geek - "...However, there's never been a noticeable difference when we've used them in group rides...."
I would chalk up the difference in feeling faster vs are faster to vibration and possible side to side flexibility of the Rolfs. On a group ride there is somewhat objective standard to measure against that doesn't exist riding alone. Feels faster is not always faster, but it may be fun just the same.
Tandem Geek "... We could easily get the rear wheel to rub against the left or right brake blocks by simply coasting while standing with the bike leaned-over to one side or the other as well as while standing and climbing out of the saddle...."
That would scare me.