rather than speed, you should keep it at a lower rpm, thats how much work your engine is really doing, i try to keep mine between 2 and 3 grand. and dont ever floor it from a full stop either, that burns more gas, you get in a higher rpm faster. goes for any car really. heres something i havent tried yet, but might be worth looking into:
http://www.jcwhitney.com/autoparts/P...?Ntt=fuel+boss
it uses magnets to give you a cleaner burn, its supposedly gonna give you 11.6% increase in gas mileage. for 22.99, it might be worth a try