Let’s see a whole week how many sigils/member are required to close the last portal (yeah leaderboard is out of discussion as Sirrian said that it’s a P2W feature).
It depends of your guild rank in GW leaderboard. Most guilds didn’t get any gems. And stat bonus for 340 gems have always been a “maybe these bonus make you win”. But only a maybe. For 250 gems, you get a new troop and a new weapon (both meh) and other stuffs.
The deviation is apparently super low (if there is no bug ).