I read this and wondered if you were serious (maybe your are...):
- Windows down
- Sometimes use A/C
- Bikes on top
- Going 80mph
I'd guess your Cd might be 0.40 - about what a Dodge Ram gets.
I drive a 5-speed Insight in the Dallas area. The first 2-3 years I'd do 80mph or more often than I do these days.
Low 40s is the mpg I got going that speed. Doing 80 must be important to you if you realize you probably could be doing 60-70mpg at 60mph.
Dallas has a lot of NASCAR wannbes too. I cope with them staying in the rightmost lane, sometimes avoiding the freeway, driving at non-peak hours. To be candid, I think you could do the same and not feel in danger.