Very little accuracy loss with the G27. Personally, like SGTMAC26, I like the G23 better as an overall choice but was pointing out for CCW you might want to look at the G27. I have both and it's hard to decide which I'd choose if I could only have one. The Gen 4 G23 fits just right while the G27 is a little easier to conceal.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek