Any of the newer 480-650w bar or board leds will outperform a 600w hps/mh by a lot. Why such small yields? You just not using much of the space?
Guessing from your post, you've have had little or no experience growing under 600w hps.
medium adjust a wing (hood), new 600w bulb and a 600w digital ballast on a light rail will cover a 1.2 m x 1.5m with good results.
guessing a 480w led will cover a 1.2m x 1.2m.
If you have enough light to cover the canopy, leds vs hps makes little difference, you save some electric with LEDS but they cost 100's
HPS are really cheap to buy but cost more to run.
I am building my own leds and so far the results are really good, I can easily change my led chips(cheap quick and easy, plug and play)
it should cover a 1.2m x 1.2m at 700par @ 14" (very even spread, no hot spots, I spread the chips out until I have a good level spread, corners drop off a little but can't fix this. The led is 364w from the wall.
I will replace the led chips every 2 years (cost about £100).
Going to use it on my next run, side by side with my 600w HPS.