Increasing the flow through your sump isn't really the best way to increase surface aggitation, and it doesn't take much to aggitate the surface either. If you were to take like 2 or 3 of those powerheads and just move them up or point them up you will have more than enough surface aggitation. Flow through the rock work and along the substrate is probably more important to worry about as that is where your filtration will occur.
You can do a closed loop and run the drains and returns over the side of the tank no drilling required. I prefer to have the drains drilled but I probably won't drill the returns again, instead I will run the returns over the top of the tank and build a manifold that sits on top of the tank and use locline to direct the flow down into the tank.
