I only ever get 87 in my 4runner, mainly due to cost per gallon, but I will soon experiment with 89 and 91 for grins and giggles.
I drive CA freeways and streets averaging 200 miles a week just to and from the office and I GOT around 14-16mpg before I changed a defective coil pack.
Extended HWY driving (to and from Reno, NV) I averaged 20mpg (before changing out the coil pack) per 450 miles leg of that trip. I have not driven to Reno since changing the coil pack.
AFTER changing the coil pack, about 2 weeks ago, some basic pump receipt/ODO calculations show me about 15-17mpg in the city. As far as HWY goes, I expect my average to increase to around 21 or 22mpg if I'm cifering my math right.
BTW, this is on a slightly lifted (1.5-2") 2WD '99 T4R running 265s with proper tire pressure.
Oh, and yes, a larger fuel tank would be nice.