I match a 600w bulb to a 600w ballast both in veg and flower. I've never really heard the change in spectrum, though I wouldn't sweat that kind of thing. The only time I really turn mine down is: 1 - to slow down a vegging plant, and 2: if it gets too hot in the flower room during the summer. So in either case, the supposed altered spectrum probably isn't really relevant.

I would be careful overdriving the bulbs, that will definitely decrease the life span. Don't believe all the voodoo shit you hear, it's just growing weed.

Peace,

Farmer Rich