All iPads iPad WiFi + LTE on AT&T is it Fast

It won't be any faster whether you tether your iPhone 5 or get LTE directly on the iPad.

However, tethering will drain your iPhone's battery very quickly, which is why I got the LTE iPad myself. You also get GPS on the LTE version.

I have an AT&T iPhone 5 and AT&T iPad 4. If you tether an iPad to your iPhone 5, the only thing that can prevent you from enjoying the full LTE bandwidth your phone enjoys, is the speed of the hotspot. I'm pretty sure that the speed of the hotspot exceeds the highest LTE speed you're likely to see with AT&T.

So the answer to your question, is that the speed of an AT&T iPad 4 will be the same as that of a wi-fi iPad 4 tethered to your iPhone 5 via a wi-fi hotspot.

Most people justify the extra cost because they either don't have an LTE phone with hotspot capability, they don't want to drain their phone battery using the wi-fi hotspot, they don't want to wait for the hotspot connection to be made each time they want to access the internet from their iPad, or they don't want to have to carry their phone every time they use their iPad out and about.