MDHS...
Do you do your training rides alone? How often did you stop, get off the bike, walk around, eat??
Will you be doing the metric alone? Even if you go by yourself...for a group ride you are never really "alone." I think if you can do 42 miles in pretty snotty weather solo....you can handle a group metric with stops and people.
Personally, I get really bored on 40 mile solo rides, which makes those rides painful. I find the social aspect of group rides help make the miles go by much more quickly. You (1) focus on stop to stop, rather than "OMG, I gotta do 62 miles!!" and (2) chat with folks, ride group to group, get on the wheel (with their okay) of a group moving at a nice clip. There are sort of "rides within the ride" that keep you motivated.
I think you'll do fine.
2007 Seven ID8 - Bontrager InForm
2003 Klein Palomino - Terry Firefly (?)
2010 Seven Cafe Racer - Bontrager InForm
2008 Cervelo P2C - Adamo Prologue Saddle