Well got the 418's and compared them with the 412's. First, the obvious the 418's are WAY better than stock, hands down.
Here were the ground rules for this test. I took my bike out for a determined course that I knew was rough. I rode it with my 412's. I then went directly and put on the 418's and took it on the exact same route.
The 418.
I could feel an immediate difference in the ride of the bike and handling of the bike. Notable difference on the small stuff and smoother on the rough stuff.
There was a stretch of road where they did a poor job filling cracks, that with stock was un-bearable with the 412's it became annoying, the 418's was tolerable. (This stretch is even bad in a car)
One thing I noticed was I could feel more through the stock front springs than I could through the back springs.
The 418's come with an adjustment for dampening the rebound of the shocks. I set out at the first setting and the #2 preload setting so that I was the "same" as my 412's. I rode down the rode a spell then moved it down to the base setting as it was stiffer at #2 preload for me (182 lbs) I then cranked up the the rebound setting and rode the rough segment mentioned and I think I preferred the 1st setting on that as well.
Observation;
They are smoother than the 412's but not as smooth as the 440's.
The ride is solid and responsive, I would have to say even better than the 412's, and I thought that they were spot on!
There is plenty of room for adjustment for heavier riders and loads to make this a great and versatile shock.
It comes only in the 12.5" and I would have to say the additional capacity actually raised my bike up slightly. I didn't measure it, but will do so when I put the 412's back on. For a step down comparison.
Here are some pictures that show the difference on my bike between the appearance of the two shocks.
eddy
Progressive 418 - America 
Progressive 412 - America 
