When you're trying to decide whether a rental is a good investment, cash on cash return seems to be the accepted method in the real estate world. Since you own it though, there's no "cash", so try doing to calcuation with a hypothetical 20% or 25% downpayment.
If you want to know what the market will support, rentometer.com seems to be pretty dead-on with regard to rent prices.
I'm not totally clear on where they get their data from though. Anyone with any more insight into that?