What's the verdict?

Been done, (and longer) obvious invalidates the warrenty & risk killing yourself when the headtube snaps off 😆

And its slack enough as it is with 140mm…

Overkill. My MX only gets fitted with Van 36's for DH/Alpine trips. Much happier with a set of Pikes or similar so on a "standard" frame why bother?

It probably won't spontaneously snap but you are pushing the limits of what it's designed to take assuming you don't just want it for riding along extreme towpath 😉

The ultimate intention is the Alps in August. Could travel reduce them to 140mm… hmmm

Loved my Prophet, probably one the best performing bikes around, instructed and guided on it, ragged it down DH courses and generally abused it….then i stuck 160mm's on it….sold my 140's and i….Quickly began to hate it, far to slack even back in XC setting on the swing arm.
Pant's downhill and uphill.

Get an adjustable if you do, i ran 55's on it which adjusted to 130mm i think but performed crap when wound down.

I'm with Skills Guiding – love mine with Pikes, hate it with 36s on. Too slack