The strait is over a kilometre deep (the Wallace line) Although there are guides on the tides and currents, they did not work for me and finding my way North near the Bali coast ( sail to land in case of engine
failure) to the wider part of the strait where the current
is less, while trying to stay in bands of less unfavourable current
before crossing properly worked for me. I have seen over 4 knots, but only in the narrow part S of Benoa.
In 2009 I spent some days in the area in May and again in July and never found any sustained northerly current independent of tide.
Also- have you noticed that many of those small fishing
trimarans are happily doing their stuff without any engine at all? It can't be that bad when they're around.
Are there any locals with better info?
Hope this helps.