You don't often increase flap without a concurrent decrease in speed.
With Slats thrown into the mix things get more tricky.
A good example is the Flap Fail/ Slat Fail procedure on the Ejets. Depending on the failed surface the optimum position of the non failed surface is as much to do with landing attitude as it is to do with stall speed.
Too nose high and the de-rotation eats up landing distance so the compromise is a slightly faster landing speed with a lower attitude on touch down.
Just saying ;-)