making the returns larger is going to slow down your flow rate. I would stick with the 1" returns but make the drains 2".
I thought this as well (it made logical sense to me at the time that having more water weight for the pump to push due to the larger pipe would decrease flow), but someone recently called me out on this. It's counterintuitive, but a larger return will give you more flow because there will be less friction within the pipe, all else being equal. The static pressure at any pump discharge is going to be the same whether there is one 1" return pipe or ten 10" return pipes, all else being equal.
Check out this link and scroll bout 2/3 of the way down to see the formula:
http://www.pumpfundamentals.com/tutorial3.htm




