Should I upgrade to a 600w?

So I've got 2.5 grows under my belt w/ the 400w mh/hps. (the 1/2 grow means that I'm about to harvest the 3rd crop!).

I'm working w/ a tent that's 2x4ft and 7ft tall. I've gotten my temps to stay steady in the mid 70s and my ventilation is sufficient.

After this grow, I'm all out of seeds and clones, plus my lease expires in the next couple of months so I wanna have everything all cleaned up in case I decide not to renew.

So I was thinking in the meantime I could do some upgrading and put together something a little more productive. I know I'll be switching my regular bubble buckets for larger containers, and I'm still just gonna do 2 plants. I know I'm going to scrog them, so I just need as much root space as I'm gonna have to have to fill the 2x4ft screen. I'd like to not have to change nutes as often.

Now here's my real question, (or set of questions).

I want to upgrade to a bigger light. I'm pretty sure 1000w would be too much for my tent and I can't grow any other way with my living arrangements right now.
Right now I'm using a 400w ballast that I got on ebay w/ a wing reflector and later upgraded to a cool tube. (i had to rewire a socket, pretty easy it seems).

Now I wanna get a 600w light, and I'm looking for the most cost effective option.
Can I just switch the ballast and bulbs? Or do I need a new socket for the 600w bulb?
Will 600w be substantially hotter than the 400w? I'm sure it'll be warmer, but will it bring a whole new set of issues w/ ventilation? Will I need to upgrade my exhaust fan?
How much more power does it use than the 400w? I noticed a bit of an upswing in my power bill w/ the 400, which is fine, but will the 600 be 50% more or does it run more efficiently?
What kind of increase in yield can I expect given that all other things would be the same? (i know this is a tough question, but I just mean will it be substantial enough to justify the upgrade, (which I'm thinking I can do for under $200).

I'll appreciate any advice anyone can give. I know I got 5.5oz off my last single plant grow, and I wanted to get at least 10oz off my current, 2 plant grow, (which I'm not sure if I'm gonna get).
I'm just a rookie that wants to go pro and get at least 10-12oz per grow.

Will the 600w make that a whole lot easier?

 

Ok, maybe I'm not getting responses because the answer if obvious.

Of course I should upgrade my light.

What about to 1000w?

Would I be able to run a 1000w light in a tent, and if so, what would I have to do to overhaul the ventilation and make it work?

I could change the fan that's cooling the cooltube from a 98cfm inline duct fan and instead use my 170cfm fan that's attached to my carbon filter now.

I could order a bigger, higher velocity exhaust fan w/ a new filter, (gonna be time for a new filter soon enough anyway).

Help me out here guys. Right now I'm cooling the light w/ this fan- High Tech Garden Supply .

I'm exhausting, through a carbon filter, with this fan-
High Tech Garden Supply .

If I used the current exhaust fan to cool the light, then exhausted and filtered with this fan-
High Tech Garden Supply , would that be sufficient for a 1000w light in a grow tent?

 

Nobody??


Will a 170cfm fan dedicated to cooling a 1000w bulb be enough to run it in a tent?

 

Thanks bud. Let's see if I can get someone to convince me that 1000w is ok.....