I think that jumping up to the C rated tires, you will lose a considerable amount of fuel economy. With the P's at 32psi, I went from an average of around 16mpg with the stockers to 10-12mpg with the SA's. I was getting around 300 miles to a full tank, and have dropped down to the low 200s. Not a good feeling. However, yesterday I raised the psi to 42psi, and the tires still handled flawlessly through the storm we had. I actually drove on I-94 at 7pm from Waukesha to Milwaukee and was completely confident the entire way. So I'll give it a week and see what it does for the fuel economy.
I know one thing that was hurting me was that around the time I had the tires installed, the temps dropped. So that's about the time that I started warming her up for 10-15 minutes every morning. I'll let you know if a week or so what my mpg findings are.
Ben