I put 12,000 miles on my car in 2 months recently when my work car was broken. I did everything I could for gas mileage and eventually got it to hit 27-28mpg a couple times. I leaned it out until it surged and then richened it slightly. I have a lockup converor and drove the speedlimit which put me ~2,000rpm.
I have a TA64 turbo and 60lb injectors. The bigger turbos should have the potential to get better (and worse) mpg due to less backpressure. The injectors, as long as the chip is burned right for them shouldn't affect gas mileage. Other signifigant things that help with gas mileage on my car is higher compression, lighter rotating assembly, running it lean on the highway, freeflowing exhaust. Things that hurt are a bigger motor (4.2L), and dragradials (maybe). Around town, with the old 3,800 stall convertor it averaged 8mpg if I was lucky. I had the convertor knocked down to 3,000rpm and it's much better now but I haven't actually measured it yet.
