"Would you not have to factor that into your monthly electricity bill and then multiply it by the amount of months you plan on using that card to see if it is cheaper, if at all?"
What a fantastic point completely unstressed by the conclusion of the article.
I will contend that, according to their PSU charts, that the power draw difference is negligible on idle and about 70 watts at full load. Since in most places you're charged something like 9 cents/1000watt hour, you'd be looking at a very long-term investment with the 4770 for value, which most likely will be an outdated card in a few years given its slower speeds in comparison to the 4850.
Again, it's not exactly an easy decision and I personally don't think that the 4770, right now at its current price point, deserves a recommendation.