Wattage Vegetative Stage

Does watts are important in this phase?

For example,if i have one 250w hps for veg,one plant under this light will grow more slow then if i have one 400w hps? and less bushy?

Hey, I had to re-read your question a few times. If this is what you mean, does more wattage mean better, faster growth for one plant. Generally the answer is yes! a 400 HPS puts out more lumans than a 250HPS. Go get a 600 HPS Good bulb to learn on and good for 6 plants in 2 gallon pots. But def upgrade from the 250HPs and if you are stuck on the 250HPS Go get a bounch of T5, those bulbs will VEG your crop sooooo much better and give u much better light distribution. And if your stuck on a 250HPS, get the best reflector u can afford, stay away from a air cooled unless you take the lens out..
HPS will give u a short bushy plant. dont let anyone tell u otherwise! Unless u place bulb way to close or to far because the plants respond to a certain pigment in the R (wat ever reading) to help determine growth height. Best luck!!! Oh, if your really considering a low wattage bulb like 250HPs, u can do really good on T5s, they have earned there respect.. Im a 1000HPS guy but the 600 has earned there respect Most ill bend! haha

Im running a 1000w mh on my seedlings all different strains.
I'm finding the growth to be short in hieght
and the leaves are getting nice and big.

Im not sure about the speed in growth.