A sword that was 7 or 8 feet long would be almost impossible to carry around, let alone use effectively on a battlefield. Swords were made that big, but it was for ceremonial reasons, or to show off the skill of the smith, since properly and consistently annealing blades became more difficult, the longer the blade was.
A blade of about 5 1/2 feet ("the height of a man" back then) was pretty much the uppermost limit for a combat-suitable sword.
The Japanese made swords called "O-dachi" (different from the similary-named "nodachi", or "field sword"), which were some of the longest swords ever made--and some of those probably ranked among the highest quality of very long blades, as well.
Here's an example:
http://japantrip.tripod.com/nodachi/odachi_gallery.htmlThis webpage has a sword, the "Kibitsu Maru", which is 337 cm in length, with a cutting blade of 226.7 cm, and a weight of 14.5 Kg, which was forged entirely via traditional swordmaking methods (as in, the blade was hand-forged as a
single piece--it wasn't welded together, or anything, and the rest of the components were also traditionally made), in the year 1447. It's the longest sword in Japan, and took amazing skill to make.