The should be a speed vs rpm chart for your car in the Technical Data section of your owners manual for both tip and manual transmissions. That will tell you the expected speed in any gear at any rpm.
My 2.5L 5-spd is doing a bit over 70mph at 3,000rpm in 5th gear and I average about 21-23mpg in steady freeway driving (70-85mph).
Here is the chart from my owners manual:
