benefits to a bigger return pump

I have a wide open 1/2" bleed on my manifold because my pump is somewhat oversized, not by much though. There is a T ball valve creating backpressure to the main tank, the manifold runs the length of 4' the bleed is between the 4' manifold on a line that meets the manifold bar at a perpendicular angle, the two sides of the 4' manifold bar goes directly to a calcium reactor and the other side to a gate valve feeding my 40 gallon frag tank. All of the piping is 3/4" except the bleed, but I don't think my flow would be very reduced throughout the manifold if it was 3/4" bleed, this would just allow me to remove my t ball valves on my main tank feed and ca rxr, and open up the gate valve on my 40.

I think the case would be much the same with a pair of pumps.

 

Plus it's not like you're relying on that scenario exclusively, you wouldn't optimize flow conditions when one pump was out, but it would keep things running until pump failure was detected and could be replaced.