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The only real downside to getting a larger tub IMO is the extra up front cost (and to a small degree the extra cost to heat it) and the extra space it takes up. If those aren't a concern then don't worry and enjoy the obvious benefits of the larger spa which is the extra space inside the tub in the X, Y and Z directions that allow you to stretch out and relax without playing unwanted footsie or rubbing elbows with the person next to you.