Interesting that your phone's CPU seems to be doing much less work with Wi-fi instead of 3G. What could cause such a thing

edit. Of course the Wi-fi test was done by night. Were you using you phone much when doing those day tests? It is not a surprise that even a passive 3g connection is a battery eater. I tested it and the battery will get empty in 15-18 hours with it.

How about doing same tests without GTalk or skype (and both) on?