Chuck it's fairly simple actually.
You do want to use Flarum. If you would consider any forum software for production environments professionally, you wouldn't take into account any software that has been recently released into stable, a mature package would make more sense for several reasons: bigger community, more extensions, less bugs, tested on a wider scale, etc ..
So.. the reason you ask this question because you actually like Flarum so much (yes!) and actually would like to turn decision making into that direction, but can't because it's not stable.
Bottomline, if you have a deadline for the decision any time soon, pick a mature software package. Especially for a "large forum" like yours.