Honestly you should still run the 80 stam (if you can clear it) since you'll probably get some bronze ones and have a better chance at the gold dragons. Long run you'll need tons of gold dragons and you'll end up selling bronze ones cause you get so many.
12-5 is really hard. I haven't tried it again but i was around 140k power and got destroyed on it. There's a lot of the roamers that just tear apart your squads.