Well Nick (How's the baby, did he or she arrive yet?), as I've said, when it comes to LED I'm no expert but I'm getting a lot of conflicting information and it's easier to believe, for me, that prosource is overstating their coverage than other explanations.
I'll explain further:
As you said, prosource's own website says, (for flower) 90w for 2x2, 180w for 3x3, 350w for 4x4 and 700w for 6x4.
However, Mathew linked a video that's clearly a prosource commercial: http://www.youtube.com/watch?v=kxPvN9ke ... r_embedded
...uploaded to youtube by "ProSourceWorldwide" which features a big grower with 400 180w Illuminators ($240,000 at retail prices) and at 7:32 he says the lights should be 14 inches above the plants which is in the range that prosource lists for the 180w...but at 7:37 he says they should be 2 feet apart, for flowering, which of course is 2x2, 4 sq feet, and 45w/sq foot. A 90w at the same area (which prosource claims) would only be 22.5w/sq foot.
That's not all. California Lightworks, maker of the SolarStorm, says their 800w light covers a 4x4, in flower, which only uses 640w worth of LED in "flower mode" which equals 40w/sq foot.
Going back to prosource specs, they claim the 350w at 4x4 = 21.875w/sq foot and the 700w at 6x4 = 29.16w/sq foot. So none of prosource's own specs get close to the 40w/sq foot that you and the guy in the video likes and, personally, I'd even prefer more. While you rightfully say that you can use a 180w in a 2x2, you'd HAVE to use the bigger light if you want to grow decent medicine which conflicts with the website claims. You'd want more w/sq foot (like HID) if you want the highest (no pun intended) quality.
Clearly, imho, prosource is overstating their coverage for their lights on their website or they're quoting specs for tomatoes or lettuce. I don't think 20-30w/sq foot is cutting it, I'm not even sure that I like 40-45w/sq foot.
At the current prices for LED and the amount of lights needed to cover an area that can be covered much cheaper by HID (I prefer 1000w HPS lights) even accounting for other needed equipment and energy, it would take 10-15 years to reach a point of ROI which is the lifespan of LED lights, assuming you don't burn out a few diodes aver the years. I'm sorry, I know this is a LED forum, but they're just not ready to replace HID in the bang-for-buck show yet.
Obviously, this is *just* MY opinion and I readily admit no personal, hands-on, growing experience with LED but I have a lot of outdoor and HID grows under my belt so I do know something about the crop and hydroponics in general. As I told Mathew there are some advantages of LED grows, many touched upon in the video. I think when the individual diodes are pushing 7-10w each, stable, AND a lot cheaper, it'll be a good alternative to HID...just not today.
Hope that helps...