I think I'm going to get a 1 1/8" tach or something, the one in the stock guage cluster is very inaccurate for me, It was so much better when I was using the Racepak, almost makes me want to buy another one.

Seriously, my tach is off by 500RPM at idle, more so higher in the RPM range.

I'd never mount a big one, but a smaller one for reference wouldn't be such a bad idea in my opinion, just for accuracies sake.