It's been pretty well covered in the responses to your two posts. The blade should be long enough to cover your tracks when angled, and perhaps stick out a little to the side so you can "reach" into ditches, along borders, etc. The only reason I can think of for going smaller would be if you expect to be using it a lot in tight quarters where you would have trouble maneuvering with the 7' blade. A 6' with ability to offset the blade may give you the best of both worlds.