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..
Anthem AVM60 Outlaw 7700 Emotiva A500 Epson 5040UB