Eh, biggest I've ever run on a brevet is 49x15, which isn't all that big. It did have me set up nicely for a 6:30 200K, though, until I caught a bad mechanical that took an hour to get resolved.

Talked with some UK riders at PBP this year who spoke of a guy they knew who was running 100+ gear inches on brevets in Wales. Hats off to that guy!

I agree with Homey re: the huge gears having their place on long rides. On a long ride on a geared bike, I like throwing it a huge gear on flat terrain and turning over a lower cadence while still keeping up a good speed. For me, that just gives everything a rest. Spinning all the time gets tiring. Heck, if you're brining all those gears along, might as well use them. Most randonneurs I see ought to just remove their front derailleur, for as little as I see them use it.