I have seen the Colt 6920 come up several times in this thread, and it seems to be rated well.
Ironically enough, I just got an email ad from CDNN that has it on sale for $1,099... Two questions:
1 - Is this a good price (i.e. what is the average going price, and what is the best deal you have seen for it)?
2 - Is this system customizable, meaning could I eventually swap out the heat guard for rails, or add optics to it?
It is just as customizable as any of the others, but will require you to add parts to it.
I have mine setup with a DD Omega Free Float rail, Aimpoint M4s, Larue BUIS, and a Surefire X300.
I went with the Omega rails because they were lighter than the MI FSB mount and Surefire 6P that I had before and it would allow me to take the light off when I don't need it without needing to rezero.