I have an upcoming marathon and tried the vaporfly next for the first time. This shoe is very stiff. I saw reviews which said it is unstable but I don't think that at all. I think the shoe is very light, very stiff and somewhat muted (compared to zoomx in the pegasus turbo). I wouldn't mind something a bit softer and bouncier... would the alphafly be worth a try? Aiming for 6:50 pace.