When I introduced the faster group Chris, against resistance from some committee members, very few signed on to it on the days. This made it harder and less accessible than it should have been. Ironically however many who started with the large 17mph group went way too fast, did not qualify, but would have had they signed on to the 20mph group!! Make of that what you will....lack of ambition, lack of self-belief, preference for disqualification, general awkwardness etc.
If you look at your club ride speeds the 20mph is a no brainer. In theory it encourages order and teamwork amongst faster riders in the club, whilst still presenting a challenge. That seems well within the principles of a reliability ride to me. Enjoy anyway, RR1 has the best memories for me, with the weather often playing a big factor!