600 is the most used light. like i said we get them closer to tops as its cooler and has less lumens loss this way. and is cheeper to run. on average a 1k hps has about 150k lumens a 600 is about 90k. but with a 1k needing to be so far away cause of heat we loose that extra 50k. roughly. with a 600 you get on average depending on hood style or size will give a 4x4 to 5x5 footprint of good light. so most go on a 1 square foot per plant. but if you flip sooner to flower can close this up a bit and fit more in there.
i suggest run clones at 3 weeks veg then flip them, makes for a faster turn over and will still produce good weights as ive shown with 2 foot tall plants inc pots of 2 gal size. i think with that one i ran seed at 5 to 6 week veg under T-12 only. so with a T-5 will need less time.