- a note of caution for Intruder and others - use of speedbrake (in a 737) with flap above 5 will produce significant and possibly fatigue inducing tailplane buffet AND stall speeds are increased (10kts) with speedbrake, so my logic says that min flap speeds need to be thought about also. Whether this applies to the 747 I know not.
Those cautions do not apply to the 744 (which is the subject of the OP's question). There IS a significant increase in buffet with speedbrakes just before the flight limit stop is reached, but little buffet before that.
Speedbrake with flap really shakes the flaps something horrible. I find it a little dismaying many pilots regard speedbrakes as a natural way to slow down everytime, rather than applying energy management.
I've never flown the 737, so I can't compare it to the 747 Classic or -400. However, the -400 is MUCH more difficult to decelerate than the Classic, and that is even giving credit for the inability to use S/B with ANY flap in the Classic.
Also, those who use S/B for deceleration MAY have read a Boeing pub that implies that S/B and landing gear are the "only" drag-producing devices. A couple Check Airmen in our company chastise Pilots for using flaps above the bug speed for drag...