I'm goning to be making a new sales thread for these, the 5.6A aluminum, and adding the option of Carclo optics instead of the Khatod. Dan (run4jc) did a great review with some OTF numbers on the quad and septa here:
http://www.candlepowerforums.com/vb...-and-other-Drop-Ins-a-mini-review-photo-heavy!
The aluminum version uses a MCPCB, copper version solders directly to the copper heatsink. That alone, before any material advantage of the silver/copper means 2-3C/W less resistance to each LED, at ~5W each that means each LED is running 10-15C cooler from that alone. Along with the copper transfering the heat much more efficiently to the host, and the fact that it can hold 50% more heat for it's volume than aluminum, means that the copper module will indeed have a higher initital output, and a longer lasting output.
If you look at the OTF values measured by Dan and apply a % to the OTF output from it's original LED output, you'll see that the copper module at 5.6A retains a higher percentage of it's OTF lumens than the aluminum model at 4.2A. Dealing with more heat, the silver/copper heatsink is still able to provide a higher thermal efficiency.
The Carclo optic tested with silver/copper heatsink did 1654 Lumen OTF. That's 93% of the orginal LED output when the optic only states 90.2% effiency. How is that even possible? Well, the LEDs are binned at minimum outputs, so the LED lumens are probably more like 1850 than 1780. You can see though, with a silver/copper heatsink, there is virtually ZERO thermal resistance. No loss from heat at turn on means a nearly perfect thermal pathway.
I don't have one of FM's C heads, but I've heard they have no lip to catch a drop-in. Apparently the glass lens is what hold it's down. I won't be making an adapter to work with this head. I suggest you get a Cryos cooling bezel from Ronac.