As Accurate? Sure. As Fast? Probably, depends greatly on the software. Customizable/features? The carpc absolutly blows away turn by turn GPS units. The CarPC isn't just a GPS, it's an entire entertainment center in your dash. You can do pretty much anything you can think of on a computer, on your carputer.
If you JUST want gps, go get a gps. If you want a new hobby and the full power and customization of a car computer, I highly recommend installing one. Store bought GPS's are a waste of money imo.