I think it depends on the batting and on how the quilt will be used. If my (decent quality) batting says 4-6", I might stretch that to 7"-8" if the quilt won't be washed more than a couple times a year.
If I expect it to get heavy use and get washed a lot, AND it's for somebody besides me, I'll stick with what the batting says.
I'm not big on extra-close quilting all over the quilt. I like to showcase the fabric and applique/piece design rather than the quilting.
I'm pretty new to quilting tho. Others will have better answers.