Heat: 400w vs. 600w MH?

I am thinking about getting a 4x4' grow tent. It seems like either a 400 or 600 MH would be the right light to do vegging plants and clones.
Does a 600w bulb put out much more heat than a 400w or are they about the same?

The set up would be vented with an 8" fan, I would be using a hydrofarm reflector with the glass shield and the 8" vent. Ballast would be electronic and outside the tent. The 8" is not as monstrous as it sounds because I split it to vent the rest of the room and the duct has to turn a corner, room does not have great inward ventilation etc.-so I worry about keeping heat under control as much as possible.

You will want at least a 600w in a 4x4. I would recommend a 600w with a dim-able ballast. 400w puts out 2/3 the heat of a 600w. Vented with pretty much any fan and you'll be fine with the heat.

Get the 600 fershure. With a 4x4 tent youll prolly want to put another 600w in there later! I have a 400w and a 600w both in cooltubes and i cool each with a 260cfm duct booster fan and they are cool to the touch. An 8" fan with any kind of air cooled hood will keep a 600w super cool