The 1K is very, very nice, I run a couple, but many people are switching over to 600w's because of heat problems, I mean with the 600w's you lose out on lumens, but it makes up with the ability to be able to get the lights closer and not having to worry about so many venting modifications. Plus 600W HID's are the most efficient when it comes to watt to lumen racial. Many people pull the same yields with the 600 as when they had a 1000, but this depends on growing skill and your set up.
In the summer when the heat picks back up I may traid out one of my 1K's for a 600W and see how it does.
Adieu