Well, I did a dumb thing - I forgot to max the controller

I missed that in R3, "Camera Speed" means look speed, and I didn't have it turned all the way up. Doing that improved things considerably, although turn speed is still a little slow for my tastes.
I also turned off "Camera Acceleration" because I found it got in the way (with the controller, that setting speeds up your look speed the farther/longer you hold the analog stick, which doesn't play nice with a mouse).
I tweaked my sensitivity down to 12.75 again since 14.75 was too much once the controller speed was upped. It works pretty good - it's not as good as the KZ3/Reach ST combo, but it's not bad at all particularly in single player. The last thing I have left to tweak is the Diag. Damp - I think the recommended 2.0 is off, my up/down speed is definitely a little slower than my left/right. I'm going to tweak this some more.
Also I've found that the online community for R3 has faded quite a bit - in fact I think there are more players still on Resistance 1, which seems to be the standard bearer for this series still. I may work on a config for that one next.