What is the biggest hill you have ever rode up on a FG? We have some very looog hills in this state. I would love to take the bike up some major passes but I'm not sure if it possible

I heard one way of finding is if it is possible is if you get on the bike and try it

Third worst case scenario is you gotta touch shoe to pavement.
Second WCS is you turn around and go home before you get to the top.
Absolute WCS is you don't bother trying.

Bring water and snacks.

Get Over It: How to Climb on a Fixed-Gear Bicycle

I've ridden this twice on my fg: Chico Wildflower 100 - A bike ride in Chico, CA
First time was on 62 gear inches, far from ideal. Second time was on 57 gear inches which wasn't much help but still better.

As everyone is saying, you just have to go for it and push yourself. Never know what you can do until you try

That thread gives the technical details. Here's the goods, from the same dude:

Paul Rozelle's 24-hour, pre-PBP, fixed-gear, Mont Ventoux ride

"Fame and glory (and masochism) aside, I believe that just about anything that can be done on a geared bike can be done on a fixed-gear. Ventoux has been climbed by fixed-gear riders before. It was probably the usual means of ascent for a long time, but that was so long ago that most people have forgotten. I wanted to restore some of that memory and perhaps inspire people to push their own limits in cycling. Doing both Ventoux and PBP in the same week would help make the point in a more extreme fashion: if this can be done on a fixed-gear bicycle, then tell me what, exactly, cannot?"

/thread

All good advice here. I've put the important parts in bold.

mmmmm

snacks

Take a look at this Seabase - Galibier on Vimeo