A Dynamo loadout with last-ditch effect. (My friend in xp2500 said it is very, very useful, and I trusted her, fully)
I have reduced the swim speed to 0.2 but it doesn't really make that much of a difference. Might be a bit hard to run away from a booyah bomb that is aiming right onto you. But a lot of dynamo players don't bring that much swim speed in general anyway.