My grow tent is 4' wide by 6' long & 6' high. I use a Sunmaster 1000 watt warm deluxe for veg and flowering. I have had great success with this. Sounds to me like you have the perfect setup as long as you have a fan for some ventilation.
I run a 1000wt in a 3'3"x3'3"x6'5" tent. I have actually ran dual 600 wys in that tent without issue. As long as you can control room temp and ventilation you will be all set
I have 2 tents , one is 4.5 x 4.5 x 7 , and the other is 4.5 x 4.5 x 7.5, i run 1k in each, i also added a 400 mh to one of them for the last half of flowering in the 7 ft one last time, with a 150 cfm elecient exhaust ,and a higher volume bathroom fan as a intake, it ran at around 80 maybee a couple degrees warmer on warm days((this is the 1400wt). i have no problem keeping it under 80 with 1k and 150 cfm exhaust, my lights were not air cooled(one is for a couple days now) and both are in basements. I am runnin g hortilux bulbs in both
I dont think its too much for the plants but they would probly get the same benefit from a 600w or two 400w because you could place these slightly closer to canopy, saving a little electricity at the same time
You have to keep in mind that with a 600 you have to move the light closer to the canopy, however...you are reducing your canopy size as well. To the poster who said that a 6 will work out better for a 4ft square....you may be right, but you will definitely be sacrificing yield, because the 600 just doesn't have to canopy penetrating capabilities as a 1K.
Its all relative...you just have to make the right decision for your situation...sometimes the 600 will be the better option, but on other occasions, it'll be the 1K.
fact is the forums are literally crawling with people running 1k in a 4x4 - I've got a 175mh + 400hps and all I've got is a Stanley blowing out the bottom - just been vegging a few months, and with ducting and the like i would feel confident with 1200w and I've far less control over environment than i would like. its significant, but not as much heat as i'd feared by far - my computer does close to 500w when overclocked!
A 1000w would give you better coverage @ 62 watts per sq ft, where a 600w would only give you 37.5. You want at least 50 watts per sq ft. The only reason i would run a 600 in a 4x4 area instead of a 1000 is if heat or power consumption was going to be an issue.