That tire pressure is a bit low I think- try between 40 and 42 PSI cold.
The larger rear tire should not hurt mileage. In fact, at highway speeds, it should improve it slightly. All else being equal, and assuming the engine is running beyond the lugging range (which is quite low on a C-14), mileage will increase as engine speed drops (by using higher gears for the same speed). At 85 MPH, you are absolutely NOT lugging that engine- it will be turning just over 3,500 RPM.
The other big differences in mileage will come from the load the bike is carrying (weight) and headwinds. The absolute worst mileage I ever got on a C-14 was in South Dakota, fighting headwinds that seemed to be about 200 MPH. Instantaneous mileage dropped from an indicated 43.X to 29 MPG! But I doubt you have anything like those conditions in New England unless you are riding on top of Mt. Washington.
You should be able to do a bit better than 33 MPH but that also assumes you are riding a steady 85, not an average of 85 with large throttle openings used here and there, for example passing cars. Accelerating from 85 MPH will absolutely kill your average mileage if it is done at all regularly on a ride.
Brian
Bike is an 09' I recently did the oversize 55 swap and though its geared down a tiny bit have noticed my gas mileage has suffered horribly. I am running 37 PSI in front and back. I usually travel at 85mph on the highway here in New england and the computer reports a steady mpg of 33... Typically when my road star got this bad it was time for a valve adjustment and TB sync... I'm at 11000 miles currently.
2 Questions...
Am I due for some maintenance, frame bolt check?
Has anyone switched to a smaller tire (if available) for taller gearing?