Another abstract document. This time from Boeing for those who might be interested.
FCT 737 NG (TM)
The use of speedbrakes with flaps extended should be avoided, if possible. With
flaps 15 or greater, the speedbrakes should be retracted. If circumstances dictate
the use of speedbrakes with flaps extended, high sink rates during the approach
should be avoided. Speedbrakes should be retracted before reaching 1,000 feet
AGL.