The std tacho is already up to the task, I take my tachs to an instrument repairer and have them re-calibrated and balanced. Because the RPM needle sweep is exponential and not linear, it is ideal to have the tach balanced and calibrated at say 6000 rpm [calibrate at a higher deflection to reduce the amount of error]. Having the needle balanced [the counterweight] assisted with free movement of the needle and not relying on additional voltage [the tach works on inductance loop] to move it. Also reduces the amount of error and also improves the reaction time for the needle to move.
Are you after a tach that represents more than 8000 RPM? The std tach cct can be modified to represent just about any RPM range over a 270 degree sweep.
A couple of years back I made a few replica 10000 RPM Nismo tachs from the std tach as a base. Still working on fabbing up the redline needle.