Funny you post this Brad as I have had the exact same concern lately.
My tank has been up for a year now and i have been running two mp10's at 80% in reef crest mode for the last 6 months. The growth of my sps frags has been moderate to high but mostly encrusting and not in height. Lately i have read a few post on various forums that some reefers have been adjusting from this mode to lagoon mode and dropping there pumps back to 50% with no ill effects and some are stating better growth results in just a few short months.
So last week i changed to lagoon mode and also lowered both my mp10's to 50%, in the short 6 days i have not witnessed any negative effects to polyp expansion and the fish seem to be more active as well.
Time will tell I guess
