Flaperon 777. Sir, you are talking nonsense. you argue that the speeds would not vary so much to be very noticeable, hidden by the different power settings for take off power.
On a dry runway, in still air at ISA, the difference in V1 for the 737-800 with Flaps five, using the same proprtional difference as the event on the A340, is 121 kts as against 143kts. I wouldn't spot the difference? Then I shouldn't be there.
Reduced or derated power is a red herring of no relevance in this argument.