the VDO rev counter cannot be as fast as the revs of the engine on the first three gears and in fifth gear I arrive very quickly at 6350 rpm on the highway
Very true...I find that changing up from second at 5000 rpm only just avoids hitting the 6800 rev limiter when having fun.

The needle on the rev counter is very heavily damped so takes a while to catch up with the engine on proper acceleration.