i have 4G turned off just to prevent it from possibly sucking my battery during the day. 3G is fine for me most of the time. until i get home 12 hours later and it picks up my wifi. it will last me about 17 hours on average this way on the stock battery. not sure how much life i would get if i never let it touch wifi, or kept it on 4G the whole day.
im usually on yahoo all day with about 50 regular txts, 5-6 calls, FB and google browsing. youtube once in a while. but the screen is my #1 power consumer.
i will leave it on 4g all day tomorrow just to see the difference.