But maybe both are issues, and even if you have a fast enough system to handle the texture streaming, you will have stutter caused by the engine's tickrate.
Correct, the tick rate is yet another element that can create poor presentational performance on top of the regular suspects. And I forgot about the horror that is MegaTexture, though I can't confirm whether this game utilizes it or not; RAGE was built on id Tech 4. It would definitely worsen the frame pacing issue if it were indeed present.
You'd think there would be an option to lock the framerate in step with that if it were still the case though.
Wasn't that why the older id Tech 5 games were locked to 60 FPS?
There already is, but it is my suspicion that the tick rate only targets 33.3ms (locked 30 fps) or 16.6ms (locked 60 fps). Go above or below either target, even for a moment, and frame pacing goes out the window. Fixed tick rates are never a good idea.