Ideal return pump flow

[Coralgurl]

What is the ideal return pump flow? I have a mag18 and I used the RC calculator to figure out my flow and it came out to 854 gph with 9.75 feet of head pressure. My over flows can handle this no problem, just wondering what's ideal? I'm thinking of changing out the pump as its really noisy and it's not vibration, I've lifted it off the glass and it's just as loud.