I have a Springfield Armory XD Compact Tactical (5" bbl, compact grip) that, when I carry it in an IWB holster, conceals beautifully. In my experience, the hard thing to conceal is the heel of a full length grip. I use a compact magazine (9 shots of .45 ACP) with a Pearce Grip extender that keeps the heel of the grip compact but gives a full hand grip at the toe. My extra mags are full length 13-round magazines with extended sleeves to give the same grip size as the full size XD Tactical.
My usual carry is a SAI XDsc, also with a Pearce Grip extender for the short mag and a full length mag for a reload. This pistol has a 3" bbl and compact grip but I shoot it as effectively as my full size service model. I usually wear this gun in an OWB holster, either a BladeTech Eclipse or a wonderful Kydex and leather holster from Firearmholster.com. As I'm 6'1", 240#, concealment either way is no issue.
I noted that you wanted a 9mm, which is a perfectly good choice with the right ammo. I'm a .45 ACP and .40 S&W guy (I started using a .45 ACP in 1968 and went to the .40 S&W when I went to compact pistols)), mostly out of old habits. Any one of these calibers with appropriate "defense" ammo will prove satisfactory.
IMHO, successful concealment of a full size service pistol is mostly a function of your holster. For many years I carried a Government Model 1911 in an Askins IWB holster. I'll consider one of the new LW Commander models from Colt as I'm very comfortable with 1911s carried "cocked & locked".
In all, your choice should be made on what feels right to you and has the features you consider priorities. With the right holster, you'll do fine.
Good luck,
FH