I've found 172s are better performers 4-up than most PA28s.
You do need to do the W&B, to check the takeoff performance at today's temperature, and to add in the safety factors, but that said - no problem.
On the other hand, there are some 4 seaters that cannot fly in IMC at all with four normal weight adults - the minimum IFR reserve fuel takes you over MTWA. The Rockwell Commander 112 is one such.