Kentucky C. In a pond (lake) your size and depth a single Gast rotary vane (0523) may (will) come up short on aeration.This depends on your BOD and goals in general Also the same size piston pump will be no different. I sell both and this is where sizing comes into play. Diffuser type and placement is critical in a large body of water with shallow depths, Deeper ponds turnover more water per surface acre than shallow ponds. Consider having an aerial view and sizing map done. This service is free and easy and available through my wedsite under the "getting started" section on the homepage. You may also want to go to the Vertex Water Features website and fill out the same information and Sue Cruz will size you a system with hose layout and all the details. Again there is no charge.Your comment about wanting two diffusers lead Bill to mention the 0523 and that is a great pump for two diffusers at your depth, but perhaps not the system of choice for your lake. Bill would be the first to suggest a larger Gast rotary vane for more diffusers than two if needed.As far as noise goes if the two pumps are in Quiet Air cabinets side by side they is no difference in the noise as I have those two systems in a display setup. I have rebuilt both pistons and rotary vanes and find either pretty simple to work on with the piston needed about an additional 15 minutes of labor on the average, Average rebuild time on a Gast is about 30 minutes.Continue to do your research and you have found a great site in PondBoss to do just that Ted