2 lights I’m looking at right now are...
HLG 320 XL V2 (x2)
HLG 600H V2 (x1)
Anyone have any thoughts on these?
You could also use 2x HLG260w v2 or v1 if you want to save a few quid. I used two over half my 8x4 (v1) Its plenty of light and I don't mean its just enough, they almost keep up with my cob light I built which was 720+ watts over other half of my flower tent.
The HLG600 I assume your looking at growers lights, its a solid light with a bit more output than the HLG550 for less money.
Difference is mainly in the 3 year warranty you get with the 550 vs 1 year with the 600.
I think the 600 is as good a value as you can get from their lights.
Timber are lovely COB lights too.
Like others have said, no need to go for broke, you can always add one light to your existing set up and add another down the road in a few crops time. Or HPS , cmh.
It doesn't matter what you add, if you increase wattage your going to increase heat and you will have to deal with that one way or another.
I really do think 2x 320w xl is a bit overkill for 4x4 but that's just me.