Readers of this Blog may believe that I'm biased against "Progressives", but only in the concept of history, definitely NOT in suspension!
I put the Progressive fork setup on the Wing June of 2013 and loved it. I had ordered the rear spring that went with it winter of '14, but it got back ordered so it missed the rear tire replace for the big spring trip last year and I didn't get it installed until after we got back from our Ireland trip this spring. I had really only rode it a short distance since, so didn't have much to say until now.
A progressive spring is more compliant (soft) than stock at the top of it's range, but is constructed/treated in such a way that the more it is compressed, the firmer it gets. It is like the Incredible Hulk -- the greater the force applied against him, the stronger he gets! (which is why a battle between the Hulk and Superman would be such a cataclysmic event, but I digress).
In the real world, this means that you have an overall better ride, and as the bike is pushed in corners the suspension is firmer. Much like a stainless steel prop on a boat (better hole shot, better top end), the result is a rare engineering WIN WIN!
Anyone that has done any form of engineering knows how rare this is -- the typical situation is TRADE-OFF. You add power but it increases weight and reduces mileage, add speed to a chip but have more heat to dissipate, etc. etc.
Indeed, in both the stainless prop and the progressive spring, the trade-off is still there, it is COST. My opinion on motorcycle suspension is that the cost is FAR outweighed by the benefit, but as in everything in the real world, THERE IS NO FREE LUNCH! Which is one reason why "progressive" politics fail, but this isn't about politics!
My verdict is that the front suspension change made a far bigger change than the rear in handling, but the rear is maybe of greater import on long rides / rough roads. It REALLY makes the bike ride nice. It perhaps adds another 3-5 MPH of confidence speed in curves as well. Which means that overall it is an upgrade that does tend to put a smile on your face!
My guess on the cornering aspects are that more aggressive riders would see more benefit because of the progressive aspect of the springs -- they push them harder, so they are firmer yet in their perception. Besides, I'm most often limited on my speed in corners primarily by either the speed limit on looser ones, or by how far ahead I can see on tighter ones -- in the moose brain, there is ALWAYS a big piece of farm equipment just beyond my line of sight!
No question I'm on the conservative side of the bell shaped curve of conservative to aggressive cornering, but based on the "catching up with riders vs being passed" sample, probably very close to the middle. As always! I'm generally the exact center of all bell shaped curves, although unlike the kids in Lake Woebegone, I'm VERY slightly BELOW average!
It was a superb day to be out for a ride. The roads seem to have all been cleared of remaining winter sand on the route from Rochester up to Barron and back. My Dad was in a talkative mood, enjoying the "Last Lion: Defender of the Realm" book that I passed on to him and remembering that WWII history that he observed as a young man. His blood pressure kept him from going over, but his two brothers served. I had a nice visit and lunch that lasted a bit over 4 hours, made it back in time for the gun club meeting and still a little fire-pit time with Marla to end the day.
Spring AND "springs" are very nice.