I agree with what Jon says above. Having built my own gauges from scratch using steppers, I don't really get the complaints that they lack torque. They are fast, precise, and inexpensive.
The one drawback I will point out for GPS speedometers is that they have to get a lock before they can display accurately. Depeniding on the conditions and software (warm-lock configs, etc) that can take from a few seconds to a few minutes. *Usually* is is less than 30 seconds, but a speedometer is one of those gauges that you generally need to be right pretty quick.
The Autometer gauges I put in my f*rd calibrated using a pulse counter. Out of curiosity I set the pulse output from my ECU to aa few different values and recalibrsted it for each of them and it was within a pulse of what my GM ecu said it should be every time.
Those gauges have some odd non-linearities though. They are spot-on up to 65, but start to diverge there. At 80MPH actual, they indicate 83.
I have been tempted by the dakota digital setup for years. It has a lot of well thought out features and just plain looks good.
On the other hand, I bought a running, driving yukon xl denali this summer for less than they cost.
