If the purpose of the ride is to survive then you should be fine with the gearing you have. Take the advice of 'it's a ride not a race' and pace yourself.
I'll gladly do hill repeats that I have behind the house (1.6 mi at 6.7%) vs some stupid stuff like:
http://app.strava.com/segments/608870
Distance - 2.4mi
Avg Grade - 8.3%
Elev Difference - 1,052ft
Climb Category - 2
OR even worse after 94 miles and ~8,000' gain into a ride:
http://app.strava.com/segments/659554
Distance - 6.4mi
Avg Grade - 6.4%
Elev Difference - 2,165ft
Climb Category - 1