I'm not an engineer but i can tell you from experience a pipe with water under pressure can handle much more flow than via gravity flow. Last I measured it I think I was running about 42 gpms through a 4 inch PVC pipe via gravity flow into the trout pond. It almost fills the pipe as it enters it horizonatlly! Maybe if it was vertical it would go out faster?

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.