I have two scp-150s in my 125, one on either end in a master/slave configuration and although I generally keep them pretty low its not too much flow for my tank. I wouldn't go any lower than the 150 if I were you.
Also, most people don't realize this but the number in the model is the length of the tank that they reccomend the pump being for in centimeters. So the 150 is reccomended for about a 5 foot long tank.