Coast To Coast Overflow

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Hey there all, has anyone ever set up a coast to coast overflow ? I am planning on getting a 4ft 120 gal reef tank & would possibly want to run one on it. What kind of cost might I be looking at ? One tank I am looking at only has on hole drilled at the overflow. I just want to ensure silent operation & be able to run any amount of flow (turn over) without any volume handling issues. Some opinions are stating that just one hole would not be enough for this size of tank ? Other opinions/views are very welcome. Please remember that I am kind of "skill" limited.
Hoping I am asking the correct questions here ?