The shannon boot is exceptionally dressy and is arguably overkill in just about any formal situation outside of a black tie (if you dare, what would Vox say [gasp]) or any other fashion forward gathering. Id wear the shannons with the sole purpose of turning some heads
I have two pairs of Galways on 82 (Dark Oak/calf and Midnight Blue/suede) and they both work with a suit. I have a pair of Shannon MTOs on order. Can't wait. But my fave is a balmoral in blue from G&G that absolutely kicks ass.
My black/cloud fits pretty well in informal (suits) days. The midnight/twilight combo does stand out a bit but its a nice change of pace. Funny thing is that people say my tan/white spectators stand out more than my blue Shannons.