OP,
If you do go with GH tunes, make sure you mention to Matt your biggest interest is improvement in mileage (assuming that is the case). I won't begin to claim that I know how Matt works his magic in his tunes, but I do love his tuning. One observation I made back when I ran "canned" tunes from H&S was the early tuning was smokey and the turbo lag was greater, but they gave me better mileage than newer tunes which were less smokey and had less turbo lag. Just from my observations (on the canned tunes), the biggest difference I could see was the newer tuning had higher EBP at partial throttle (to aid in the responsiveness of the turbos) but I am sure that is a factor in why I didn't get as good of mileage with those tunes. I am sure Matt's goals are no smoke with minimal turbo lag so if mileage is the most important thing to you, he may alter the tune slightly to help with mileage although that might mean sacrificing spool up. Matt is great about providing tunes for your liking (as long as you don't request a smokey tune) so I am sure he can help you get what you want.