I had a FJC, and I think it performed great off road. I think it is a bit lighter duty in build, but it is a good bit smaller as well. I think the FJC is a lot lighter in weight (it feels like it) than the 100 too.
These are just my opinions however. Properly built, like a properly built 100, you can go just about anywhere in a FJ Cruiser. All vehicles have SOME faults, but luckily we live in a great country where we can solve those factory design flaws, and rebuild them into the true trail machines we love.
That's about all I have to say on that