With the Chev it's 75 or the speed limit, whichever is less. On occasion it hits 80 on a downgrade or if I'm passing. At least I no longer get run over the highway. The Ford seemed to struggle to maintain 65 with the same trailer.
Edit: thought I should mention I run S637's that are rated to 75. If I had the OE tires it would be 0mph. Not in a hurry really but I'd rather be at a camp location than driving on the highway.