yes 1000w in veg is just a s signifigant as in flower, meaning it can yield faster veg times and larger plants in that time. so long as the police dont come knocking at your door, and you can pay the bill there is no such thing as too much.
^^^^^^^^
What Poly said plus heat issues. Veg is extremely important to your plant's all around outcome. It's arguable, but in terms of heat and efficiency (bill) 600w is good IMHO...OK, maybe not so humble.