Yes, I'm serious. HPS is missing a large portion of the light spectrum and as a result grows nice large single dimensional tasting and ok but not great potency buds. HPS is a great choice for a main light, but if it's your only light, it's a mistake, even if you get a fancy bulb that gives a bit better spectrum. Mixing in a bit of 6500k LEDs/MH or Florescent and UVB bulbs and you would be amazed the difference in quality. If you supply 70% HPS, 20% 6500k/MH, and 10% UVB you will be impressed by your results.
That said, 6x 600w HPS = 552,000 lumens
The most you want per sqft in a system without CO2 is about 8000 lumens per square foot.
At 9x5 = 45 sqft that would be 12,226 lumens per square foot, well into CO2 required for benefit territory.
Best setup for his space would actually be, IMHO, 2 1000w HPS lights + 400w of CXB3070 6500k LEDs, + 200w of Tanning or Reptile UVB 10/9.9 bulbs.