I like to retard timing a little on the base line over 2000rpm so it burbles nicely on over run. I then have my "over run fuel cut" on a 5 sec delay so it burbles for a bit then cuts fuel and goes to a "flat" over run exhaust tone.

I am yet to venture into setting up an AFR table with closed loop fuelling. My AFRS are pretty consistent, there is the occasional spike or drop now and then which when i try to map out it makes the car drive horribly. So I'm fast learning that once it drives nicely the AFRs to a degree are irrelevant.