I've already tested this extensively:
Comparing the Battery Life of Droid Razr vs. Droid X
" On Droid Razr, when using a particular app, battery drain is 4G > 3G > WiFi.
On average, 4G drains battery about 10 - 20% faster than 3G, doing the same activity. (This is not to be confused with 10 to 20 percentage points.)
On average, 4G drains battery about twice as fast as WiFi when watching streaming video (the most data-intense activity you can do on a phone.) "
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