I have a pretty decent supply of CXTH laid in, and yes, IMO they are the toughest carbon ever made. CX was aware of this, but I think they were dropped more so they could introduce a couple more expensive types like the Maxim.
But to answer Barney, I also have some CXTLH on hand which I use primarily for my Reflex Caribou, and after doing some fiddling with Stu's Calculator and some testing I can advise they tune nearly identical to CXTH. The rub is they are much lighter.
My primary arrow is a CXTH 4560 29.5" with 50 grain insert, 125 grain point, 7" wrap, 4" para, and Super Nock, which weighs in at 520 grains.
I made up some CXTLH that match up in spine but to get close to the same weight, had to use 6075s. They are 6075, 30" 50 grain insert, 145 grain point, 7" wrap, 4" para, and Super nock, which weigh 526 grains.
I have never used weight tubes, but I think there's no question I would have to if I wanted 4560 CXTLH made up identical to my 4560 THs to be anywhere in the ballpark as far as weight goes...
CX Rebels with Weight Forward are very close to TH's in terms of GPI weight and from diddling with Stu's Calculator, look to be right in the ballpark as far as tune goes. Don't know how they stack up for toughness, though.
The CX Heritage are much heavier GPI than the TH, I have tried them and don't like them for that reason.
Yes, 5/16" brass inserts work in the TH, TLH, Rebel, Heritage, ect by CX.
BTW, TH Selects can be found on that auction site. Someone must have a warehouse full as they are selling in 2-4 doxen lots...