Having looked at the Geometry tables I’m pretty sure when the time comes I’ll be replacing my 456-SS with a 45650 or a C-45650 (when it inevitably comes out), and I’ll most likely be doing it a bit at a time, Frame, then fork (Quite like the look of the X-Fusion REVEL at the minute) then eventually wheels I expect, it’s only 1/2 an inch difference in BB height, marginally less if I did use slightly bigger 26″ tyres…
I also quite like the option of using different wheel sizes on the same bike for different types of riding, lighter 27.5″ wheelset with ~2.2″ tyres for longer distance and general duties, heavier duty 26″ wheelset with softer, chunkier rubber for Uplift days and DH Ragging, that slight drop in BB height may help the handling a shade, maybe extend the fork +10mm to accommodate the rougher stuff and raise the BB marginally.
It’s worth remembering that dropper posts and adjustable travel forks mean frame Geometry and wheel diameter aren’t really the only variables that affect how a bike rides…