I was pricing some of these strips on Digikey this morning and noticed the Bridgelux EB Series Slim Gen 3 strips are available. Looking at the data sheet, it looks like there are some pretty decent advances in both performance and efficiency with this version.
The nominally output 4980 L running at 700 milliamps@ 38.2V = 26.8 watts. One of the interesting things in the data sheet is that you can overdrive these by LARGE amounts, with the maximum drive current of 1.7 A .
Over-driving LEDs for the longest time has been a rapidly sliding scale of what you get in terms of light vs what you waste in heat, this is a characteristic that all LED manufactures obviously want to improve. It looks like these strips basically have linear performance gain up to their maximum current rating… See here
So basically we can drive these strips at 1.5 A for a 200% output from nominal. i.e. 9960L without a crippling decline in efficiency, providing of course you heat-sink for decent thermal dissipation… i.e throw away heat fast enough via a decent heat sink… That works out $14.81 USD for about 9K lumens 
These are only 12.7 mm wide so could be run side on a piece of 25mm C Channel 4 mm Aluminium…
Pretty cool IMHO. I think I will get some.