I don't think you are going to notice a huge difference in 5-6ft. I always measure from the center of the tweeter. I actually think the best location is to try and have the tweeters at ear level when seated, but that is not always possible for everyone.

How far back will you be sitting and how far apart will the speakers be from each other?

Welcome by the way..
_________________________
M80s-VP180-QS8s-EP600-2xEP350 Denon3808 Outlaw7700
M22-OWM22-VP100-Denon2805
Audio Nirvana