The fact that you have a single return line effectively limits you to ~45 GPM; that rate matches well with your filter.

The Hayward MaxFlo XL that Mark mentioned is a good option; it's available in a 2-speed model that will save you quite a bit of money: Hayward SP2307X102 1 HP Max-Flo XL Dual-Speed Medium Head Pump

The flow rates match your setup well:




Complete info here: MaxFlo XL @ Hayward-pool.net

You may need to install a heavy duty 3-way toggle switch for the pump, to allow you to switch speeds: I can't tell if the motor comes with a mounted switch or not.

If you are going to purchase the pump directly, you probably want to rule out Pentair pumps: they've reduced the warranty on their products to 30 days, when sold directly to the end-user.