Some 60 and 75mph measurements

I know it's hard to compare numbers and I'd love to have a hypermiler drive my car for a month to see what is possible and in how good a shape it is...

The next best thing is probaly to have clearly defined testing conditions.
Did some long, boring runs on cruise control, so maybe I can put them to good use . In the Netherlands, so flat as a pancake. Wind negligible. Tires 36-38psi. Measured on GPS. Temp 60-65F (~15-18C), no rain, both with ~500pound load total. Fuel useage is from the Priusscreen, so a correction might be wise: average according to my Prius: 5.2L/100km (45.2mpg), according to fuel data (see sig): 5.45L/100km (43.2mpg)
So the Prius seems ~5% too optimistic.

60mph (98km/u) 4L/100km (58.8mpgUS)

75mph (120km/u) 5L/100km (47.0mpgUS)

The 60mph was a full half hour without any noticeable difference between the 6 bars. Resolution is 0.25 or 0.2l/100km (so I was stable between 57.4 and 60.6mpg for 30 minutes).

The 75mph were 'only' 5 bars (then I ran into heavy traffic). Stable between 46 and 48mpg for 25 minutes.

I have the pics to back it up (although you won't see the speed...)

I could try 50mph, but I'll have pissed off lorry/truck drivers passing me and possibly flipping me...

 

Thanks, that's a great help for me, as I long for confirmation my car is OK. I worry because I can't get even close to the numbers some of you get. E.g. the 2000km run on one tank of gas is simply impossible, as my driving out of town (while warming up the engine) averages about 7.5L/100km (~32mpg). As a wild guess the warming up of the engine uses 50% more during the first 5 minutes than driving normally. That alone would empty my tank with the amount of engine-starts she did long before reaching 2000km...

F8L, the engine was warm (having driven at least half an hour before) and the HV filled to 6-7 bars. With fuelprices darn close to 10$/gallon I am not going to drive an hour just for testing , so a vice-versa run can rarely be done unless there is several hours inbetween (hence no guarantee the wind is still the same). I'd still like to stress that heightdifferences of more than 100ft are rare in Holland, I'd be surprised if I even had differences of half that in my runs.

I'll try to give 65mph a try. That should keep me well above truck/lorry speeds yet still (almost) within the 100km/h (+ 5km/h legal correction ) speed limit.
(Highways have 100km/h (62mph) and 120km/h (75mph) speed limits and recently a new 130km/h (~82mph) limit that simply uses too much fuel on both cars to warrant me using this new limit )