well I have heard of 30mpg in a very mild 2.4 with a very mild cam, MSA 6-1 header, and early SUs. The owner was an older gentleman that obviously knows hot to tune his car.
don't know what ou mean confident. If your drivetrain is solid then it should be fine to drive that far. If your 260 is like mine no. I have no insulation , header-2.5 exhaust, turbo muffler at the back. After 20 minutes of driving constantly at 3500rpms you can't really hear.