This is what it is all about: What sounds good to you.
Set your speakers to large and play with your sub and crossover settings, then do the same with the speakers set to small. Which sound do you prefer, it's YOUR system!
FYI: My B&K Ref 50 is set to small speaker size (all 5 channels) with the crossover set @ 80.0 Hz
High Pass Slope: 12.0 db
Low Pass Slope: 12.0 db
LFE Level: 0.0 db
Crossover on subwoofer on bypass, volume knob slightly under 1/2 way up.
Main Seakers: RF 7's Center: RC 7 Rears: RF 3II's Sub: RSW 15
I let the sub do the lower frequencies because I think it sounds alot cleaner, even though my RF 7's are perfectly capable of reproducing them.
Correct me somebody if I am wrong but room size and layout contributes to this equation also.