You can run 1" from the pump to a 3/4 reducer into the bulkhead and run 3/4" loc line. That's how my aquarium is plumbed from the factory. I don't think you'll see that huge of a difference in flow especially since your pump is still rated at more than your overflows can flow. I think you'll be fine with what
BIG-G
suggested. If I were drilling my own tank I'd do it like that to give feed both over flows