I'll give away a hint at the results of my experiments by saying this: round two ended up being the final round of testing, and the theoretical winner in the contest of iPad2 WiFi versus first-generation iPad with 3G and WiFi is: the first-generation iPad.
More details about my constraints and decision criteria can be found in part one, but the basic rundown is: I want to know whether an iOS device without 3G or GPS could serve as a navigation device for traveling if tethered to a device acting as a mobile hotspot.
Yesterday's test results were slightly promising but inconclusive, largely because I didn't actually leave home to perform the experiments. Today's experiments were to test maps on an original model iPhone in «airplane mode» (meaning with the cellular radio turned off) but WiFi enabled and my Palm Pre acting as a WiFi hotspot. The difference today is that I would test in a place without any nearby WiFi networks.