It is relative to the size of your growing area and to the maintainable climate/temperature you can provide.
If you could maintain good ventilation to your area, and 600w is your maximum, run the 600w HPS for flowering.
I use 50% strength of my MH for veg, which for you would be the 250w MH and double for flower (600w HPS for you)
The more light the better, but only if you can handle temperature effectively.
Not uncommon to see 400w per plant

The tradeoff between heat on a 400w and a 600w is minimal, but the lighting is worth the small amount of extra power used (easily compensated in extra harvest)
50% less power in MH vegging trades off light, but is compensated by spectrum keeping the nodes short and growth healthy
Cheers Jimmy.