rpm at 70 mph

If you own a smart phone, the torque app / Bluetooth obd2 reader will get you all the information you ever desired.

The the stand alone scan gauge II is also an excellent monitoring tool.

 

I forget but it's nowhere near 2,500rpm. The Prius runs at a ridiculously low RPM at freeway speeds.

That being said, the actual RPM is going to be based on load because of the eCVT nature of the power split device. So it's not like an old school fixed gear transmission. 70mph driving can be done at 1,000 to redline depending on the load. Toyota Prius - Power Split Device

Honestly, don't worry about it. You're not going to hurt the ICE. I'd worry more about the battery and keeping the transaxle fluid clean by changing regularly.

 

2400 is not uncommon I use a scangauge II

 

While not uncommon, that is well above average, and indicative of acceleration or hill climbing. At least it is in the Liftback, the 'v' wagon likely has a higher RPM.

I think in flat steady driving at 60 mph, RPM spends most of its time between 1300 and 1600. Wheel and engine speeds are not directly linked as they are with traditional transmissions, so RPM will rise faster than proportionate to road speed.

 

Why does it matter if the engine is designed for it? The computers will not endanger the drive train components.

 

I just came back from a road trip, mostly at 70-71 MPH (~51 MPG indicated) and RPM ranged from 1000-2700 depending on grade. I'm not good on spotting a flat road in hilly terrain, but it looked somewhere between 1700 and 2300. BTW, the speedometer was 1-2 MPH high compared to GPS.