I've personally made the mistake of buying either undersized, or buying brands that do one thing well (veg) but not the other thing (flower) LED fixtures.
Expect to pay between 400-800 USD per fixture to sufficiently cover 4x4, depending on what brand & what features you need.
I'd recommend any of the "basic three" brands which would be Vipar Spectra, Mars Hydro or Spider Farmer. These are like the Toyota Camrys of LED fixtures, but I dunno if you've seen a Camry lately but they're pretty frickin sweet
lol!
I recently won this awesome light here on this forum:
Mars Hydro FCE 4800. I was in the market for one anyway but was lucky enough to win it. Two of these would FUCKING SLAY a 8x4 with not much added heat. They're like $430 right now but no doubt there will be a 4th of July sale coming up. I highly highly advise, no matter what, get this bar style and not the quantum board older style like this one:
This is the Spider Farmer SF4000 old style, I was borrowing it. Great light, SUPER intense but generates more heat & a wicked "hot spot" center under the light, bar style has way more spread. Go bar style for sure.