They use the same network and speeds will vary depending on how AT&T allocates bandwidth.
Too much is made out of theoretical speeds and not enough about actual, "real world" results. All carriers (and ISPs) throttle bandwidth depending on various factors (network congestion, area, population density, etc.). And you'll likely see no difference between the two devices in terms of network performance (or a negligible one). If you'd like to test the speeds, you can always download Speedtest.net Mobile (by Ookla), found in the App Store. But be careful how you interpret those results. Carriers are known to throttle data differently (for example, Bell Canada, at one time, throttled App Store downloads more aggressively than other data).
As for the badge, it is reflective of the device's technical capabilities. The iPad 2 was not marketed as supporting 4G speeds (unlike the iPhone 4S), which is why it does not present the respective badge. However, this is more of an artificial marketing strategy than an accurate measure of network performance, which as described above, will vary depending on many factors.