slayer thanks for the imput,well heat i dont think is going to be a problem as im set up in the basment and in my 4x4 tent its runs about 60 65 being about max light on''low but brings out the fall foliage''.dont trust those dam space heaters....im really aiming the question at effincey and ease for mantince the 1000 in the 56x56 just seems alot easyer to handle using less space my 600 works vey well but i get the light within 8'' from the tops and lose covrage basically if i can pull pritty much the same yeild in the smaller space then thats what ill go with hope im makin some kind of sence.......set up is just shitty so many options 
My .02 cents:
If cooling is not an issue... A 1000 watt light over a 4 x 4 in the 56" square tent would produce the most light per sq foot. This is a classic, efficient setup for 16 plants turned down at 12" - and will produce 2 lbs from most strains. Low yielders like OG, etc will still produce a pound or more in this setup.
- at the highest quality.
600 watt lights are the most efficient (most lumens per watt). Currently - there are no 600 watt MH bulbs. If you want to run both MH and HPS from the same switchable ballast - 1000W is a better choice as both MH and HPS lights are available in this format. 600W MH conversion bulbs run closer to 400W MH performance. If running only HPS this is a mute point.
If you have room for a 4 x 8 tray in the 4 x 8 tent - that would be a more efficient setup - and will likely produce more bud than the 4x4 with a single 1K light. BUT - 2 600's over a 4 x 8 has considerably less lumens per sq foot and the quality and yield may suffer as a result.
A 3 x 6 only offers 2 more sq feet than a 4 x 4 - but 2 x 600's over a 3x6 would bring the lumen to lumen rating closer to that of the 1000 over a 4x4. The extra room offered by the 3x6 may come in handy for other equimpent.
