I was in the B737-800 sim the other day.
Low vis take-off at MTOW (79 t) and 15 kt quartering tailwind. ( 10 kt TW, 10 kt XW). Engine failed shortly after V1. (They're mean aren't they!)
No significant terrain ahead so engine out procedure was simply to track straight ahead with a standard acceleration altitude of 800 ft AGL.
During the flap retraction, I held the vertical speed at zero so there was no way we could have accelerated any quicker than we did.
Guess what. We didn't reach Flap Up manoeuvring speed until we were almost 30 nm from the aerodrome! It seemed to take for ever!
Now in this case with the visibility being so low, it probably did make sense to clean up as there was no chance of returning for a landing. A diversion to "return airport" was the only option. But imagine if the weather was fine and there was an engine fire, or severe engine damage. You're going to want to return for a landing as soon as possible. Over weight landing? So be it.
How can flying 30 nm away be safer than simply accelerating to flap 5 manoeuvering speed, keeping the aircraft close to the airport, and getting the aircraft back on the ground that much more quickly?
Don't forget that the extra time spent accelerating to flap up speed, can't be used to get much else done in the flight deck. Both pilots should be making sure the aircraft is flown correctly.
So for me, it's a valid question worthy of discussion.