You will want to test a power out situation. When it is all set up, cut the power and wait to see were your water levels go. Water will siphon from the display tank and go into your sump. If it looks like water is going to overflow your sump you will need to raise the return in your tank a little higher till you feel good about what your water will do in a power outage. Just make sure you test before you lose power...
Scott