In reply to Kahti:
Its pretty hard to do a decent resole on a Solution with C4 as its too stiff and thick to make a decent hollow shape - it's possible but you tend to deform the shoe more than I'd like, plus you already have a second layer of rubber on the SOlution so you end up with something quite clumpy. The Solution comes with XS Grip2 in 3.5mm, the C4 is 4.2mm and that's a huge difference. Even putting 4mm Edge on a Solution is not great.
The Vapor Vs are a fairly stiff construction inside anyway so you wont see a huge difference with the rubber change. Depending on which version of them you have they have either Edge or possibly the old Grip (the Grip2 is far better imo).
C4 is definitely stiffer - its pretty obvious to tell when you have them all as sheet rubbers - but it does make a difference which shoe you put it on. Anasazis have no stiffening in the shoe, even whites, so they totally rely on the rubber for stiffness (which is why they soften up so quickly). Scarpas and Sportivas all have a separate mid-sole stiffener if its meant to be a stiff shoe so they hold their shape and feel a lot longer.
In terms of gripiness, everyone has their own opinion as which is best which I think comes form the reality that there is very little difference between them.
Thats my 2 pence worth anyway, hope it is of some use.
Torquil - Llanberis Resoles.