Opinions before i start

Hey all, i am starting a 4x4x7 grow soon and hoping to gather many if not all supplies this week. My only problem now is deciding what light to use in that amount of space. Should i go with a 1000 watt hps or a 600 watt hps? I live in a very cold area so for the next 7 months and am not too sure if heat will be an issue but want to plan ahead for next summer.

1. 600 watt or 1000 in a 4x4x7 tent?
2. If going with a 1000 watt what size ducting/fan/filter should i get and what cfm rating should the filter and fan be?(thinking at lease 8inch and cfm of 450+)
3. Will a 1000 watt give me significantly more of a yield than a 600 watt or would the trouble with heat diminish the yield greatly
I will be venting everything into an attic

Thanks a lot for any help and i hope that as i live in this free state and learn with experience, i will be able to pass valuable knowledge to others.

1000w is going to get that tent hot, I use a 600 in my tent.More light the better but most will say 600 for a 4x4 tent.

My room is 4X5 and I use a 600W light. You can always get a 3.5 foot reflective hood to cover more area in your room if you think it's necessary. I also use a 560 cfm exhaust fan pulling air through my reflective hood. The ducting size depends on the hood you get.