Going from the stockers it's an easier call Howie. Just one upgrade step and no reduncancy. I still want to see how much they're going to cost and couple that with a good idea of the general range of handling improvement.
My Progressives are good. In fact pretty good. I'd find it hard to justify another 800-1000k dollars just for shocks that are a little bit better. At some point good enough really is good enough.
My thinking is that a good shock is a good shock. The Progressives are a big improvement over stock because the stock air shocks don't have much damping in them to start with, but many people are very happy with the stockers. Those that have switched out to something like the Progressives see a good improvement, but those shocks are still limited in what they can do.
What do you get if you choose the Bitubo's over the Progressives?
1) More spring pre-load range, the 440's have 3/4" and the Bitubo's have right about 1.5".
2) Compression damping adjustment, to prevent teeth shattering jars from bottoming out over bridge abuttments. A passenger can easily adjust the compression damping while riding if necessary.
3) Rebound damping adjustment to prevent topping out.
Would I do these instead if I had stock shocks? Definitely. Would I toss a good pair of Progressives for these? Probably not, but if I had a good number of miles on the Progressives, I'd have to think about it real hard.