In general use, the fourth-generation iPad is plenty snappy, though for most tasks you probably won't see a huge difference between it and the third-generation iPad. It's a testament to Apple's engineering that iOS and its built-in apps have been always been more or less smooth, regardless of the hardware.
Among the other improvements on the newest full-size iPad is souped-up wireless capabilities. Like the previous model, the fourth-generation iPad has Bluetooth 4.0 and supports 802.11a/b/g/n Wi-Fi flavors. However, Apple brags that the new Wi-Fi is twice as fast as the previous version, thanks to the addition of channel bonding. In practice, I didn't notice exceptionally faster performance for tasks like downloading a PDF over the local network or grabbing a TV episode from iTunes. In most cases, the Wi-Fi of your device probably isn't the bottleneck, anyway.
Finally, Apple also upgraded the LTE chip in the fourth-generation iPad, providing support for more LTE frequencies around the world. Like the iPhone 5, the iPad comes in two flavors: a model with support for LTE bands 4 and 17, which works with AT&T here in the U.S., and a model that supports LTE Bands 1, 3, 5, 13, and 25, and works with Sprint and Verizon (it supports CDMA in addition to GSM). Also as with the iPhone 5, the CDMA model's broader band support means that it's the iPad of choice internationally (though that depends on your ability to find a supporting carrier). And, unlike the Wi-Fi-only model, the LTE version also has assisted GPS and GLONASS, which help provide more accurate location services.
Fast as Lightning
As mentioned above, the only external difference between the fourth-generation iPad and the third-generation is the change to Apple's new Lightning connector. My colleagues Jason Snell and Dan Frakes have covered this topic most ably in their reviews of the iPhone 5 and iPad mini, respectively.
The smaller, bi-directional nature of the Lightning connector is a nice change from the old dock-connector; its somewhat more compact cables are easier to to throw into a bag, for example, and it's nice not to have to worry about which way is up. If there's a knock against the connector at present, it's that it doesn't have the same breadth of accessory support as the long-running dock-connector port.
I did test the iPad with a couple of adapters, specifically the Lighting to 30-pin connector, which lets you use older accessories, and the USB version of the new Lightning Camera Connector kit. Both worked as expected. With the 30-pin adapter I was able to play music to a speaker dock, as well as charge and sync with my iMac. The USB Camera Connector kit allowed me to import photos from a digital camera and my iPhone 5. (I even built a horrifying Frankencable by connecting the USB Camera Connector kit to a 30-pin-to-USB to a 30-pin-to-Lightning adapter, though all it would let me do was import photos from the iPhone to the iPad. I'm just glad it didn't set either of my devices on fire.)
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