[Suzerain of Sheol]

Honestly, anything over 4 pounds is going to have you gasping after 5 minutes of swinging it, let alone be terribly unbalanced in most cases. The biggest zweihanders got up to 5 or 6, I believe.

A well-forged sword should feel practically weightless in the hand. If you had someone freakishly strong, you could give them a slightly heavier weapon as long as the mass distribution was on par with a lighter blade, but for the average fighter, the general rule is 2.5-3 for a 2hander, 1.5-2 for a 1hander.