I don't see how skipping sea hag hoping to get upgrades through is good here. The thing is, every sea hag I play is another upgrade play you need, until the curses run out, and I'm slowing your economy a little in the meantime. And later on the sea hag will upgrade to something really useful. Now, two sea hags isn't worth it, I *think*, because you aren't giving out more curses really, and you do want to get that upgrade train rolling.
Further, silver/sea hag is going to hit 5 once decently often anyway, a lot more often than silver/silver gets 5/5, especially given chance of disruption by sea hag.
5/2 split is more interesting.
Well, anyway, there's always science....