Ask a Warrior Thread.

Actually it won't always easily outweigh. If the speeds are equal, the shield has to make you greater than 10% stronger to overcome the multiplier.

So a sheild with rather high w.atk, really good potential as compared to your other gear, or a medium w.atk and a medium potential is required.

Yeah, but the chances are that your weapon speeds won't equal (unless you have Speed Infusion). One-handed swords generally have the advantage of speed, making their DPS higher easier with a good shield.