One thing worth mentioning, if I'm carrying an aux I'll generally have a tank to go with it too. Say your main fuel is contaminated, or your fuel hose is damaged, then with a backup tank you'll still be able to get home
True it's more space, but worth it in my opinion!
And 2.5 should be more than enough. It won't get you on the plane
but it will get you there eventually!
Bugger it I'll buy paddles
5.4s paddle quite nicely off the front, a good technique if trying to talk to and follow wayfarers round in very little/nae wind