I am getting a couple expensive carbines in the next 2 weeks so I'm not going to be bidding on this one, but I don't think $4k is out of the Question.
CCNL #110 has Q-EX 10 as the COM and it is almost exactly like this one. The barrel on Q-EX 10 is a RO and the front sight is a N,and 10 is blued but that's about it for differences. There are some QHMC traits that are specific to them and the one in the auction has them.
Dave