PreserveFreedom,
I have both of the guns you are talking about. Assuming you are looking for a PDW weapon, I would recommend you make your decision on how you plan to carry the gun. Although I like my 27 alot (its a great shooter) but its kind of an awkward size in that its smaller than it needs to be to wear on the belt, and bigger (wider) than it should be for pocket carry, ankle carry, or some other "deep" concealment. The Kahr MKs are much better at deep concealment.
The 29 is completely inappropriate for the deep concealment but is just right for belt carry. It is, as they say, a handfull of gun where as the 27 is small enough to make a speedy presentation a challange. With the hotter 10mm ammo the 29 will perform balistically as good or better as the full size G22 with the long barrel.