Short answer: it sounds like it's less aggressive.
Longer answer:
The IIC+ mode, applied to the III, is called the III+ mod, and several people here have gotten it and said it was an improvement. It does make it somewhat less aggressive, but it's important to understand what that actually means.
I've had a blue stripe III for about 30 years and, for the most part, "aggressive" to me seems like another term for "bright AF". Like, too bright. A lot of people run their presence controls between 0 and 2 as a result of it.
There are several good threads on the topic, here's one of them with some really good information spread throughout http://forum.grailtone.com/viewtopic.php?f=3&t=27879