Well. I have 27,5" rims and 3" Suomi Fat Freddie studded winter tyres.
Just installed them as we still have snow and ice here.
There are only couple things I have noticed so far. Fat Freddies are way more bouncy, because increased volume. Almost acts as a secondary suspension (1 bar / 14 psi)! The height of the tyres are almost identical to 29" with butchers on.
Maybe you could say that it is little bit more nimble... Hard to say... What I am sure that rolling resistance is bigger as expected!
Anyways I am going to switch back to 29" when possible.