My power continues to build right up until the nanny cuts me off, so I try to shift somewhere just short of that. That means I was starting to think about shifting to fifth at 125. There's no reason I can think of (when I'm pushing for power that is) to shift up until the gear I'm in starts to run out of power. Get going fast enough (140? I have a spreadsheet showing some theoretical shift points somewhere around here) and shifting up to 6th would be in order.
Its not that I don't use 5th and 6th, they are nice cruising gears that help push the mpg up... I just know that when I want the go juice it's down in 3rd until 88-96 or so, and then 4th for a few more seconds (it really doesn't take long to get to 125) and after that I really can't say from experience.
On-Ramp pull is 1 2 3 6, I never even glance at 4th or 5th, since I'm only gunning it up to 70 or 75, whatever speed traffic is moving at, then right into efficiency mode unless I need to pass or something.