Perhaps I wasn't clear enough
- I have to award round 1 to Centaurus here
It was
"The command speed bug is set to the target speed you will be flying on the approach for both manual flying & with the autopilot engaged. So you set the speed you want to maintain - in your 1st example, 138kts"
which contradicts the Boeing 'advice' and indeed highlights the dilemma that advice is known to cause.
I NEVER bug Vref+5 with autothrottle in anything above a 'zephyr day' since the sometimes wild attempts by the a/t to maintain its 'programmed' margin are often too much to tolerate (for a sensitive soul like me). In fact I normally prefer manual throttle in gusty/windy days which makes the bug setting EASY.
Boeing left us with the "what do I do with the bug when I disconnect the a/t" puzzle - I need, say, Vref+10 but I am bugged at Vref+5.