I dunno about larger tires like 225, but I've found I can run my 165's at 51PSI (max sidewall) and still not have abnormal wear patterns. Does anyone make LLR tires in that size?
The biggest improvement you can make to freeway MPG is to slow down a little. Driving to Montreal over the weekend, I decided to take it at 50mph instead of my normal ~60-62, and was rewarded with a huge improvement.
This image was stolen from another member here on Ecomodder, but my car's numbers line up almost exactly:
