How good are lower wattage HPS? 70w-750w

I have recently found a 70w hps light with the fixture and i guess the ballast is inclouded since its an outdoor light that's plug and play. How good will this be to bud??? I would go out and get a 400w HPS if i had the room 4 it, but that's not happening. Has anybody ever used lower wattage HPS lights with succes???
The same question about the 150w hps???
Maybe if the possitioning was better???

room is 2'x2' and i have about 5' to work with going up

well think of it this way im sure its better then cfl and they produce quite well. im sure they well be better.

I use a 70w as a supplement to my 400w light.
It does fine. I just got it because it was so cheap.
Don't expect anything crazy, but it put out more lumes/watt then cfls with better spectrum for flowering. Probably equal to almost 4 of the 23w cfls as far as lumens.