I've got a 60G 40x18x20 tank. 
 
I'm running 2 MP10's.  One on either end of the tank in anti-sync mode.  I get really good random flow patterns, very few dead spots, and I can vary the flow depending on the coral requirements.  
 
1 MP10 likely won't be enough for a 50G tank unless you are going for a full soft coral tank.  If you want SPS you will need more flow IMO.  
 
I don't think an MP40 is overkill for a 50G tank as it puts out just a bit more flow than 2 MP10's (both on 100%), but the benefit of syncing 2 10's together would be better than just having 1 MP40 IMO. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
	 |