I would run the 600 @ 24 " - And get a Lumin Meter(cheap on Amazon)
https://www.amazon.com/gp/product/B004K0A7I6/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
Then measure @ canopy- takes out some guesswork + google lumins and cannabis for best range-Wanna say 65000- 85000, but had great results @ 45000(milage may vary)
Nutrient range in Hydro at veg. should be 700-800 PPm based on 5 scale -any higher in Hydro, risk lockout/ burn, so your good there+ add hydroguard, assuming your doing hydro(best insurance Against Root Rot) Hope this helps I'll measure mine tonight(lumins) and let you know. The hand test doesn't work- I've light burned plants when I could put my hand 2" from cooltube- Its intensity- sure old school MH/HPS got freaking hot- with Cool tubes ,not so. Two different kinds of burn_ i burned My WW. early with LED I could put my hand on(showed up as yellow tips) then you have to read rest of plant, in order not to be DR. cannabis and diagnose Nute burn/ def.
Here's the chart:
http://www.marijuanapassion.com/forum/showthread.php?t=43715
Scroll down and chart gives best figures