Somebody could run statistics on the games for the past year or two. You’d need a decent sample size because the G1 turn and even J1 turn (if you do J1 attack) can swing it a good bit.
As a relatively newcomer, I’ve got little idea as to what a fair bid was. I heard 8 and went with that.
The bid might also depend on your level of play. It’s possible that one side requires more skill (though I’d have no idea who, other than the first G1 and J1 attack turns being a bit overwhelming if you are new).