If you are stripping them back 6-8 inches there is no way you can maintain the charactaristic impedance of the cabling. The cable is designed with the pairs being in very close proximity to one another, and as speed increases this becomes a more important factor (some manufactures put a plastic divider in there to keep them right where they want them.
Generally 1/2" is achievable, that is what we strive for since some installations are Cat6 and some are Cat5e, we just always strive for that. At any rate, it should be the minimum possible to do the termination correctly. When you have failures in testing at higher speeds, they will generally be at the termination points. The first Cat6 we did, until we realized how absolutely anal you had to be with the connection, every other one or so would test out. Once we did a few to see, and figured how tight the thing needs to be, they went fine.
Are you punching them down on a 12 port rack that fits as a 66 block would into an 89B backplane? Those can get very cramped if all the wires come in from one end, care must be taken in termination indeed but it can be done.
Good Luck! It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com