GPS accuracy with Wi-Fi only iPad

I have a first gen iPad 3G, which obviously has a cellular chip built into it. My understanding is that the GPS capabilities are integrated into that, and always work even without a data plan. Which is how I can still get accurate GPS with Wi-Fi only. I only used the data service for specific travel events, but $130 extra might too much for as little as I would use it. But, how accurate is GPS for Wi-Fi only iPads?