I've been offered a full size 9 mm pro for my 40c. I am trying to get out of buying 40. Ammo. Will the fullsize be a lot harder to carry?  I carry the c in a crossbreed. Should I just keep the c and upgrade the ejector to feed 99 better through the factory 9mm barrel I have?  One thing about having the 40 and the 9 barrel is that if ammo gets short I can shoot either caliber.

I guess it will depend on what your definition of "concealed" is.

If you define concealed as 100% undetectable regardless of body position, then yes, anything bigger will be hard to conceal.

If you define concealed as undetectable when you're standing or sitting, but might print when you reach or stoop, then maybe.

If you define concealed (as I do) as being covered and don't care if it prints, bulges, or even occasionally is exposed, then no.

I agree with Mainsail.

Ive been carring a full size .45 OWB for two weeks now and loving it, ive been in close contact with close friends that didnt have a clue it was under my shirt.

Ive been mountain biking with a group of guys three diff. times and knowone noticed till i said something.

I just wear long loose shirts and its GTG.  Its alot more comfortable than IWB with a smaller pistol.

I carry and prefer full size pistols.  IMHO a good quality holster and some minor wardrobe adjustments make all the difference.  FWIW I usually carry my midsized S&W M&P .45 ACP in an OWB Galco Combat Master holster and love it.  As for your pistol swap dilemma, I'm not familiar enough with the pistols you mentioned to give a solid opinion.  FYI I have no connection to the above companies I just use some of their kit.

I carried my FS 9 (with a TLR) from October-April this last year in a Phantom with the standard OWB loops. I wanted to get a compact for the summer months but had to take summer classes, which wiped me out financially. I just recently started carrying it IWB the last 2 weeks with the standard loops removed and replaced with Comptac hooks. I was worried at first but it's been 100 degrees the last week and with just a tee shirt and shorts it does great. I'm not even using a belt, which would probably make it way better.

I carried a M&P 9 FS IWB for a few years. Concealing it standing is no problem, but it definitely prints more when bending at the waist. I could also feel it more when driving.