I say it can't hurt to give Six Gap a try. I did it last year after only riding the front 3 a couple of times (considered to be the easier ones) and, while I was slow, I managed to finish. I borrowed a derailleur & cassette from a friend's mountain bike to give me some nice, low gearing. Then I just tried to keep my feet moving so I had enough momentum to stay upright.

My advice to make the cut-off time is to get at the front of the pack when they start the ride. Last year, there were so many people, they did a wave start. I didn't get going until at least 20 min into the ride. I made the cut-off but it would have been nice to have that extra 20 minutes just-in-case.

You'll have a blast! There's so many people out there riding with you and the scenery is so gorgeous that you almost forget how hard the climbs are.

PS - love your new screen name!