
And you can input the numbers into
HERE and also change the tire sizes to see the effect on speeds as (with a little elementary math) calculate the differences as a percentage to figure out what kind of mpg increase you could potentially get.
Edit: Not sure if you could do a full tranny swap (might now bolt up) with an 03-07 Accord, but I've read that all of the internals are interchangeable. So if nothing else you could either swap the internals or do a 5th gear swap. I realise it's a lot of work though.