Interesting thread; to know which lights would suit you better, you'd really have to know what your growing foorprint is.
I currently use a 1K in a 4x4 tent, and am going to expand by 1-1.5K watts sooner rather then later, and have been debating whether to go to 2 1Ks over a 4x8 table or 4 600s over four 3x3 tables.
The biggest issue is that there aren't too many tents that are 8x8 (not 9x9, need 8x8 exactly to fit), whereas there are tons that are designed to hold a 4x8 tray.
But just for the record, anyone who doesn't think that there's a sizable difference in yield and coverage using a 1K as opposed to a 600 is sadly mistaken.