I mean it is a serious price jump for a 5x5' but then you ensure real full surface area coverage and your system will be super efficient you can even get away with running at less power than the equivalent light for a 4x4', or you could also choose to operate it from a lot further away by using the extra juice and increasing the distance.
this is precisely what i do. the only difference is when i built rigs, they were custom sized to the space to stuff as much as could be done, and the grower used active dimming.
anyone can do the same thing with a good quality commercial rig now, as long as it has dimming. you'll never run the rig full, or draw the max, leading to lower bills. i've found that's where the difference in cost savings are.
if you get a good brand the newer tech can do more with less wattage than what i'm presently running as well.
for a simple physical size i look for a rig that leaves about 2 - 4 inches perimeter between the light and the tent or grow space wall.
the plants have nowhere to hide lol.