A 4.25 inch is still " close enough " geometry to JMB to be plenty reliable , but that's the limit .
Answer # 1 & 1.5 -
The 0.75 inch can sometimes make a difference , with certain styles of OWB, when carried under a shirt tail .
* For Me * , who generally dislikes IWB , a 5 inch 1911 is rare exception . But I'm a fairly big guy , and also minor differences in body contour make bigger difference than general " size" . But it's not inconceivable for someone that a Commander might fit their butt cheek better .
Answer #2 - A Combat Commander has a different balance in the hand than a 1911 . The balance point is closer to the hand , and balances more akin to " modern " LE Service size pistols . So personal preference .
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As to size/ weight ? Modern market preferences favor small & very light . But historically , the concealed carry of full size duty type guns was common , and obviously possible . Obviously a good belt , and reasonably good holster are important , and a certain catagory of clothing . ( For me , that's already my regular non working wardrobe , but YMMV .
The flatness of 1911 does render advantages over say a 4in K Frame .