Trust me friend
Your gonna do better than your 600w hps.
Last lights I ran in my 5x5 was a 1000w hps next to my first 315 hps. I put my 1000w HPS into my 3x3 tent and grabbed a 2nd 315w lec for my 5x5; hoping it would be enough, For a 4x4 i'm sure its plenty, but the 5x5 has an extra 9ft^2; and can easily take another LEC315. I feel like I went from 1600w to 1200w, but I also ran that hydro tent at way too high PPM and had way too many tops per plant.
Next time i'm gonna run like 4 tops a plant with 3x LEC315, i'm sure thats gonna turn out grand!