thats what im running right now. no complaints. biggest advantage over 600w HPS is higher PAR and better spectrum for better terps and resin production. you will notice a difference in the quality of flower over HPS its not massive but it is there.. dont expect much difference in heat or yield though. as for a 1000w in my experience you would be going backwards trying to run 1000w in a 4x4. i ran 1000w in a 5 x 5 and it was just too hot. even with a big 250mm fan pulling air through the tent and a seperate 150mm fan pulling air through cool hood.
LED's are a really good option too i reckon. my next light set up i buy will be LED strips i think because you can actually build a set up pretty cheap with strips