Rearview mirror better decoupleable? / When accelerating BAB 5th instead of 6th gear?

Hey guys, it’s me again. That it doesn’t get boring, I also have 2 questions with me. 1.) With me the rear-view mirror always vibrates quite well when driving faster. On the BAB I sometimes don’t see so much anymore at a greater distance. Is there any way I can stop it? I drove the days with my mother’s Colt, the rear-view mirror is virtually free-floating, as far as vibrations are concerned. 2.) When I speed up or drive up on the highway, it’s meaningful. full, for greater speed increases to use the 5th instead of the 6th gear? Example: From 80 km/h to 130 or 160 km/h. 5th or 6th gear? In the 5th gear I have about 2 liters more consumption on the current consumption indicator and am at approx. 4.500 rpm at 160 things. However, I accelerate 2 to 3 times faster for this until I have reached my speed. Thanks for your help.