Depends on what you're going to put in there. Some fish like a long tank so they have room to swim, while for reef/aquascaping more width is more better.
Unless you plan on some type of carbon dosing, or frequent water changes, a large sump at least half the size of the display is a good thing. Bigger is better.
RR is better and safer than an overflow box, but not as good as the new ghost type, like "reef synergy", "coast to coast" or others, which use bean animal type plumbing. Fail safe, dead silent, and takes up way less room in the display. Not to mention less bubbles make their way to the sump, making protein skimmers more predictable, less salt creep, less evaporation, etc.
A well planned tank and sump makes all the difference between a tank that is enjoyed, and one that constantly needs attention.
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