Man, all of the Zebralight models rock!
I finally have my sc600w in hand, and was just comparing it to my sc51w - both have great tint and beam quality, and the UI is the best of the many lights that I own (I don't have an HDS yet, though...). A bit hard to tell right now, but it looks like the beam may be a bit cooler than that on my SC51w, but it still renders colors very well.
One surprise in picking this light up after using my sc51w: based on other's comments, I expected the sc600 switch to be firmer than the sc51; however, it is much more so than anticipated. I've found myself getting inadvertent high a few times, and double clicking to switch within a mode requires conscious effort - the switch will take some getting used to (but I can't imagine this coming on inadvertently).
Regardless, this has definitely been worth the wait! I'm excited to eliminate the darkness tonight.