> It's well known that accelerating rather quickly to your cruise speed is the optimal strategy for fuel efficiency, hence the reason to switch from 3rd to 5th gear directly.

I don't mean to be pedantic, but I think your logic is backwards here, ie. It's well known that 5th (top) gear is the most fuel efficient, hence the reason to accelerate to it rather quickly (the optimal rate would vary between cars), I think would be more reasonable.

I don't think the cruise speed factors into it, and neither does switching from 3rd to 5th, unless it's part of the strategy to get to 5th faster.

But then again, I never realised that accelerating harder to get to 5th faster is actually more fuel efficient [1], so thanks for the heads up!

[1] http://www.popularmechanics.com/cars/a6827/6-driving-tactics...