Everyone I've ever spoken to has said that the 100/3.5 is a disgustingly good lens from a technical perspective. I personally have never encountered distortion with my 80, but apparently the 100 has none whatsoever, and is somewhat flatter in its projection. I don't particularly care, or notice such things in the type of photographs I enjoy making, so I've had no reason to hanker after one.

But like I said, everyone I've ever spoken with who has one won't shut up about it.