AMEX prequals are typically pretty solid. Their core cards have the more stringent UW standards, so the fact that you are showing up pre-qualified for BCP/BCE is a very good sign. Your scores look good, I see no reason not to pull the trigger if it's a card you want. It's never 100% guaranteed approval, but I think you probably stand a good chance.
I think you have a very good shot. But I would let the youngest card turn 6 months, or at least let your Discover reach one year. You'll probably squeeze out a few extra points.
Definitely agree that odds are probably very good. I would just say to research the cards (asking questions here is fine and encouraged) to find the one that best fills any voids in your current lineup (regardless of preapproval status) and has the rewards type that makes the most sense for you. For example, it appears your other cards are cash back cards and while Gold may have great return on grocery and restaurant spend when redeemed for travel, if you want cash back as statement credits it's going to essentially be a 2.4% cash back card on those categories which isn't stellar.
