Wow, you've got a lot of options there...but realistically, I think you're at either #1 or #5 (or as Dizz suggests, some combination of those two).
I'm a 7.5 captain too and believe many of the 3.5s will get the bump as well. And, like you, we just missed the playoffs. What you don't mention is how many of your 4.0s...might get the bump too. We'd probably lose one (and she'd be hard to "replace"...skill- or temperament-wise)...so I'd expect a gaggle of 4.0s, half of which are "new". Not something I'd like to take up to 8.5 (where we'd already be giving up 0.5 an NTRP point per line).
And in fact, that option isn't even really open to us. We had no takers to form an 8.5 flight at all this year. And with the new 40+ leagues being run at the same time and having to compete for some of the same players and certainly courts...I don't see it happening again next year either.
So, I'm stuck with a troupe of 4.0s.
I've already gone with Option #4. Told everyone....no team from me next year. Shame, that. I genuinely liked all my teammates and would have liked to make an even more serious run at finishing, well, first.
Good luck with your decision and keep us posted on what you decide.
A 3.5 masquerading around with a 4.0 mask on.