Yeah i have a 3 3/4 in ch tach, the one that they sell on they tuse to sell it in this website infact:)!
It is made by the some company that made my gagues, so wheneer I invert the colorado or dim them, my tach automaticly dims and changed color too.
I would rather have the whole tach and shift light together, than a big red christmas tree lightbubl hangin there.
But thats just me, you just need to be careful on which one you choose. Make sure that if you get a tach, that it will be the same coloras as the current gauges that you have right now.