If i were you i would change half those bulbs in your T5 to the bloom bulbs. I would think the 600 hps would yield more but ive never flowered under a t5 only veg. so i cant really give you a definite answer. You can get the T5 alot closer to the tops so who knows. 600watt hps , 648 watts T5. should be pretty close
PJD said it best. Change the spectrum of your T5 Bulbs. Your Veg spectrum usually 5000k plus is what your plant wants until flower and probably what you have on there now. Get some 2700k to 3700k bulbs for red spectrum and maybe run 3 bulbs of blue within 9 bulbs of red. You will and would see a difference.! This is the same reason why LEDs are so effective. Better light spectrum for cannibis. You can do the research and see LED will produce higher THC content than HPS because of a better spectrum. THE HPS though beats LEDS (as of now) in Light Density and therefore wins the Yield race everytime. Change the bulbs watch the magic happen