You might find some posts on this in Tips & Tactics.
IMO the Planesman is the most important sailor on a sub (besides great engy/s), so I would class on time. Also a boost would help.
The Sonarman could be classed later after the first promotion.
Don't forget, UK sailors get +2 rep/rest anyway.
Engie stat ONLY works on Engineers.
I've only got UK SS4, but from what I've seen/read, the SS5 is disliked mainly due to only having 4 forward tubes & no rear. Mind you, it could fit 4 engys.