Congrats on your new G20! Mine is my favorite pistol to shoot. The more i shoot it, the more I love it, especially with the right ammo. You will want to reload...'nuff said. ;-)
But on to your point, some will argue against an AM bbl to begin with but I have extensively used and found the KKM Precision to be excellent (in my .40's ,also). They've always been truly 'drop in' for me, reliable and accurate. I've seen mixed and inconsistant performance with LWD but i'll defer comments about those to those who've extensively used them. Bar-Sto's are more expensive and some require fitting but in my experience don't perform any better than the KKM's. Also, I've had various Underwood ammo brass smiles with my G20 stock 4.6" bbl and springs. Then I simply switched to a KKM and shot the rest of the box with no smiles. So I feel more confident in the KKM shooting high pressure loads. On another note, I use a SS 22# RSA to help lock in those cases long enough to contain pressure. After countless rounds of all kinds of ammo, I've had a handful of FTF which was likely d/t my own loads. IMO, if the bbl caused the FTF's, they'd be more frequent.
I use stock sights but i mostly shoot IPDA distances and practice/test @ only 45'. But I have mepro tru-dots on my CCW. (G23 Gen4) Only down side I can tell is the front sight is a little tall. But it fits into my IWB holster. I just bought my first G29. I may put the same sights on it as I plan on using it for CCW as well.
Sorry for the dissertation!
That's my story... others MMV.
Enjoy safe shooting with your G20!
Armalite M15/YHM 20" 5.56