I ran regular in my 05 most of the time and it ran great. It's really a wash as far as cost goes. I might have seen 1 MPG difference when I used premium over reg and yes, I reset the computer when I ran premium and ran it over several weeks. Here's a small spread sheet with examples of miles per year, cost per gallon and yearly fuel costs.
As most people here have already said - Bottom line, just enjoy the ride
Gas $ Miles MPG Gallons Cost
3.00 12000.00 20.00 600.00 1800.00
3.40 12000.00 21.00 571.43 1942.86
3.00 12000.00 20.00 600.00 1800.00
3.40 12000.00 22.00 545.45 1854.55
4.00 12000.00 20.00 600.00 2400.00
4.50 12000.00 21.00 571.43 2571.43
4.00 12000.00 19.00 631.58 2526.32
4.50 12000.00 19.00 631.58 2842.11
4.00 5000.00 19.00 263.16 1052.63
4.50 5000.00 19.00 263.16 1184.21