I've owned a G27 for 4 years, in which time it has been my daily off-duty carry piece and my back-up piece. I shoot with it every month (minimum 150 rounds). It has
never jammed, misfed, or stove piped on me. It is most definitely the most reliable gun I have ever owned & I am extremely happy with it. (7,200+ rounds

)
My department carries the G23, I've only been with this department for 10 months (having transferred from another). I also shoot this monthly and as of yet, have had no problems with it.
As a primary/ back-up combination, you can't do much better. The 27 will accept 23 magazines, which is a plus.
My one recomendation is to forgo the standard plastic sights, especially if your agency uses the Safariland 295 holster. You can have the gun come equiped w/ standard steel sights or night sights (highly recomended).