6A CC does make sense for the Boost HX. They’re not claiming best output of the HX, they’re claiming 1500 lm. Acebeam is claiming 1650 lm. Not much between the two and those are just claims by now. I think Acebeam is just a bit more optimistic with their numbers.
Here’s a test of the HX that EasyB did a couple of months ago.
So at 6 A the HX could deliver that output. I see very little gain from driving it at 8 A or even 9 A. I don’t think Acebeam are driving that emitter at 9 A either. Even 8 A would be a lot for a manufacturer. I’m not a fan of driving LED’s at their peak in the lm/A graph, because of variances between one LED to another of the same type, lifetime, very little gain, etc. From that point of view I think 6 A to the HL is a bit much in the T9R.
For me, the differences in head diameter are very little, but of course every mm matters when it comes to throw range. Just don’t make the T9R 66 mm in your next post. 
I hate to disagree with you Tom, I respect you a lot, BLF legend. 