Do you have a sump? The only issue I see is heat so long as you acclimate the tank to the new lighting slowly. I have zoas sitting on the sandbed directly under a 250w and some sps further up, My condy is huge and has not moved since I placed him. They are all growing and colorful. 18 inch deep tank with ~2 inch sandbed. Light is about 11 inches off the water.
iirc most MH reflectors light a 24x24 inch area so for a 48 inch tank 2 is a must. I think your idea for lighting is good.
With all that said. 2 150s should be just fine.
Just my noob opinion. lol
Do you use the honeycomb limestone in any reef tanks as a main source of biofiltration?
I ask cause I have access to some awesome large pieces that would look great.
I ran a 800gph powerhead, AC70, and a 20 gallon HOB filter modified to be a surface skimmer in my 20L QT/frag tank and everything was growing like crazy and the fish seemed fine with plenty of PVC L's on the bottom.