Own a 245 (and a 226), but not a 220. Love both my SIGs. And, coincidently, the 245 fits all my 226 holsters (same frame/slide profile, just a little shorter). Not sure if the 220 has the same profile. (?)
I've never tried to conceal my 226 -- I'm on the skinny side, and I put Pachmayrs on it (so it's extra-fat). Comfortable enough in a shoulder rig, but IWB is out of the question.
The 245 carries well IWB (strong-side hip). Never felt the need to swap out the grips, and I've never used the 220 mags (although I did make sure they fit).
Only times I've had to leave the 245 at home were clothing related (pants too tight, belt too skinny) -- took my 1911 compact in a paddle holster instead. Subjectively, I think the 245 is "more concealable" even if it is a bit thicker (YMMV).