Growing indoor first time

Im just wondering, in an ideal situation, meaning everything is optimal within my grow room, with 1000 w MH for veg and 1000 w HPS lights for flowering, what is difference in my yield from 600 w lights???

hope sum 1 answers this coz ive just jumped up to 1000 from 600, but i havent heard anywhere if thers an exact formula to gauge this, im kinda hopeing 25 to 35% increase, but thats just a guess.

Isnt it .5 grams per watt for HID lights?

From what i have read 2 400 watt HID lights are better than 1 1000 watt light because its more lumens and more coverage. Its also 200 watts cheaper to run.