Laird Theramgon Tlam SS 1KA04 or DS 1KA06
http://www.lairdtech.com/Products/Thermal-Management-Solutions/Thermally-Conductive-PCB-Materials/
That said I have seen the data sheet for the Opulent thermal prepreg (many years ago) and I remember it being very good.
Before I started using any volume, I did my first ones the old fashioned way. I asked nicely for a bare board sample, and like any good hobbyist I rolled my own using my trusty printer and etched my own.
"What works with one LED will work with another." .... not true. I regularly use FR4 with vias for Luxeon Rebels and I used to use it for Cree XRE. I never use it for Cree XPE/XPG. Rebels and the XRE have a large thermal path that I can take advantage on on an FR4 board. On the XPE/XPG, there is almost no way I can spread the heat out on the surface, so I need to have a low thermal resistance downwards first and foremost.
"I am using what has started to become an industry standard for LED construction." ... and what would that be? Since last time I checked, LED on FR4, metal core, and direct thermal connection to the heat sink are all regularly practiced though you run into more patent issues with direct thermal contact unfortunately.
How do I know what those meters do? I asked! No no yesterday, but when I was looking at meters. They do not adjust for spectrum or color temperature. They simply adjust the gain (in s/w) based on a calibration done with standard sources .... which is great when you are measuring standard sources but no so great when you are doing other things.
You are contradicting yourself. You claim to be trying to achieve "the best possible". So why even discuss circuit boards? Best is direct solder and/or ultra thin high thermal conductivity glue direct to copper or even better a graphite/copper hybrid.
Yes seriously! Showing experimental results without understanding what they truly mean is useless. I did work with someone who had ruled out FR4 as being no good. What was really no good was his implementation.
Will there be an improvement between ablated ceramic and non ablated ceramic? ... of course there will be! Yes you can shave off the ceramic, hopefully you do not damage the part, hopefully you create the exact same thermal interface conditions with the non shaved and shaved version, etc. OR ... you could find out the material (or assume it is some aluminum/beryllium oxide derivative), find out the characteristics for that material, estimate the width of the thermal path, and then calculate fairly accurately how much improvement you will get thermally based on how much material is removed. That may sound complicated, but it really is not and it would not be susceptible to measurement error such as not having consistent mounting to the heat sink. The calculations will tell you it is worth doing (or not) and then you test it out. If it is not better in the test, then it is likely the test implementation, not the concept. However, if you just did tests, you could assume it was no better.
My glass is niether half full nor half empty.
I have worked with many good "feel" engineers and they are great when things are simple, easily understood and when you were not truly pushing the boundaries. However, their lack of proper methodology ususually was their (and ultimately the companies) downfall when things got complex and/or difficult.
Trust your experience ... I do too. But I am not arrogant enough to think that I do not make mistakes and/or I can't find better ways of doing things .... just like my GPS tells me often of routes I had not considered .... yet my experience sometimes knows that traffic will make certain of those routes unviable.
What was that assinine comment about the K2? In fact, older gen LEDs would benefit more from proper heat sinking that many new ones. Older LEDs generally had lower max Tjunction and they had worse output response w.r.t. temperature. The real change with new LEDs is that they are on small packages not much bigger than the die itself and hence you no longer have what is essentially a copper heat spreader. So yes now, more than ever it is important to get the LED connected to something that can spread the heat out as quickly as possible since your contact surface area is so small.