Well, as far as the Sig Sauer pistol line goes a P226 is about as full-size as you can get ...
Too large to effectively conceal?
Depends on the person, their concealment method, their manner of dress and their activities.
I used to IWB carry Colt pistols and K/L-frame revolvers as off-duty weapons. Never really found a IWB holster I liked enough to use for IWB carry of S&W N-frame and Redhawk revolvers, though. I'm not a large guy, though, being only 509/170.
That was some years ago and nowadays I'm one of those folks who prefer to carry smaller weapons, and OWB or pocket-holster carry, at that. I think it was some longer motorcycle rides which finally made me put away the last of my IWB holsters.
Just depends on what you want are willing to do to effectively lawfully conceal a P226 which is approx 7.7" in overall length and 5.5" in overall height. A good holster goes a long way toward helping in this regard, but only you can decide where the line must be drawn between necessity and comfort. There are trigger points to be found in the Glute/hip area.
Now, practical and effective concealment can be fertile ground for many a discussion and debate.
Standing straight in front of a mirror with the outer garment artfully draped 'just so' can make it seem that effective concealment has been achieved. Walking outside into the real world, however, with its wind, twisting, bending, turning, stretching, reaching, sitting, climbing, pushing, pulling, lifting, crouching, etc, etc can reveal some potential holes in that 'achievement'.
Sitting for long periods of time in a desk chair or vehicle seat can also make for some revelations for some folks.
Then there's that whole selection of garments which don't make you stand out and seem noticeable among the crowd because you're the only one wearing an untucked button up shirt over a t-shirt in sweltering summer heat, or some other combination not being worn by anyone else around you. Or, one of those newer popular 'tactical/action' shirts ... or a 'camera vest', etc.
In the several years before my retirement, and now especially that I'm retired, I became increasingly interested in balancing my selection of an off-duty/concealment weapon so that I could engage in my favorite activities on my own time, and yet still remain armed with a reasonably useful weapon.
These are personal choices and no matter which way you decide there are always going to be folks who tell you there's a better choice you could have made.
Individual choice and personal risk assessment.
Now that I no longer have the need to anticipate invoking full-time peace officer status to become involved in an off-duty enforcement action my choice of concealment weapons leans more toward the basic personal protection range of weapons.
I understand the reasoning behind the old 'comforting versus comfortable' discussion, but I sometimes feel that is taken a bit too far out of context for some needs and anticipated circumstances. I'm no longer going out on patrol or carrying caseload where I'm actively looking to serve an arrest or bench warrant on some known armed & dangerous person, parolee-at-large, etc.
What will work best for you? Only you can make that determination.
Don't be surprised if your decision changes and evolves over the course of a couple or three decades, though. It happens to rest of us in one way or another.
I still have a few boxes of holsters in my closets. Most of them very high quality, too. Just not used much any more.
I would you feel free to share your thoughts as your thinking and experience may evolve regarding lawful concealed carry methods and weapon selection, though.
Just some of my thoughts ...