3 would match your HPS watt for watt, but 2 should give you great results
I just harvested 6 ounces from a 2'8"x2'8"x6.5' tent running one 192 x 3 Marshydro Reflector that's a true 345 watt draw. Now I know the plant limit for that space, I expect I can hit 200-250 grams in that space with that light. I've decided though that Grams Per Square Foot is more meaningful. It tell you your total productivity for your size space, so my goal current goal is 1oz/sq.ft.