yupyup, my DC2 has the 10k rpm tachometer. The higher the rpm
=> you can "drag" each gear to a higher speed. Thus speed will
not reduce to lower than that (as compare to a 10k rpm) when you
drop your gear mah. 
For example with a 10k rpm tachometer, you can drag your 4th gear
to 135km/hr but for the 12k rpm tachometer, you can drag your 4th
gear to 150km/hr. Wouldnt the latter be better when you down your
gear from 5th to 4th?