What is the maximum speed my car and cruise at in terms of rpms for an indefinite period of time without risking problems?

My car is a 2003 Honda Element with 4wd automatic. The car has 160 hp with 161 ft lbs of torque. It redlines at 6500 rpms. At want maximum RPM can this car sit at and still last me 300,000 to 400,000 miles? Can it cruise 4,000 rpms with no problems and still last me up to 300,000 - 400,000 miles or chances are it won't and it would overheat?

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