Can we trust these star/round MCPCB boards ? most 16mm boards that come with XML will not have better thermal conductivity between aluminum & pad
I did a quick measurement with a 16mm and a 20mm star. The leds were mounted on a big alu heatshink, and were driven at 3A for 2 minutes.
Brightness drop was ~6.5% with the 16mm Dino xm-l, and ~5% with the 20mm T5 xm-l.
heatshink
Dino xm-l 16mm initial brightness: 920lumen, end of the test: 860 lumen
20mm xm-l T5 initial brightness: 880lumen, end of the test: 838lumen
920 lumens from 3A? I'd have thought we need 4A+ for that. Cooling must be a big part of it.
Did you measure the temp of the heatsink?
920 lumen but this is pure emitter lumen without any limiting factors, like glass lens, reflector.
Just take a look at the cree datasheet, T6 can provide 910-975 lumen at 3000mA.
The heatsink was only slightly warm, not more than 35°C.
I got 2 pcs “U2” from dino. They are T6 not U2 as I measured. One led is salvaged from a light, some thermal glue stayed on the bottom side of the star, and there were 2 solder blobs on the ± solder point. Typical dinodirect…
You better be getting a partial refund for that. U2 is priced about $1 higher.
Screw DD. Fasttech just added these T6s... for just a bit more than DD (buy 3+ will lower the price a lot). Now I can finally be off DD for good! 
Yay.