Eric I did this on my Mazda; I went a slighter better ride and went to a taller profile tire and in the process dropped a little less than 100 RPM's which in my case got the motor out of an RPM band where it was rather boomy.

Look online there are final drive/speed RPM calculators all over the internet you can plug in tires sizes and see what size you'll need for a given RPM. The ultimate method of course is a 5 speed overdrive, you can lower the rear gear to 4:11 for acceleration and the overdrive will drop the revs..........but in the meantime play with the numbers online.

Now keep in mind an A-series engine will run at 5500 RPMs or more all day long..........if it is a case of engine noise inside the car but some insulation material / Thermal barrier materials made for cars. I think Thermo-Tec is a brand of insulation. Again the motor doesn't care and the gas milage is fine with stock gearing but interior noise on our cars is an issue.

Tom

I am looking at decreasing my freeway rpm in 5th gear at 65-70 mph to some sort of comfortable level under 3000. The only way I thought of was going with a 15" wheel and a tall thin tire to increase the rolling distance. Has anyone else done this?
I figured I would make a few improvements to the power output of the engine to make up for the loss of power in 5th and hopefully increase the mpg while at it. And I also would find away to make the spedo correct.