I've only flown 4-up in a basic trainer once - it was a PA28, and one of the four was my 12-year-old (and small for her age) cousin. Fuelled to the tabs, which came in at just under the max allowable weight. I don't recall any CofG problems, so if that's a problem with your C172 then it may be worth checking out the PA28. I do remember that it used a hell of a lot of runway!!!
FFF
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