Never used unlimited fuel. A normal patrol for me usually only takes about a week anyway, so I always have lots of fuel left upon returning.
There are too many convoys in this game (even when using RUb 1.43)!
I always expend all torps after a few days of waiting in the AM sectors. Hehe...
Great fun though.
Oh, and I normally go to my patrol grid at ahead full (XXI). Never did many patrols with the IX boats though, as I suspect I'd be sent too far away then.