Antec cases are always a safe bet... not ever the best(in my opinion) but they do make good choices. The coolermaster cases are also very good... I have the HAF932 and it is amazing. I was looking at the Lancool k58 and it was very appealing, but the HAF went on sale and I couldn't turn it down. I hear good things about the HAF 922 if you don't want full tower.
Yes an 850w PSU will use more power from the wall than a 550w, even if its 50 cents a month which is negligible, however the added cost of buying an 850w vs 550w isn't and it is still overkill. And just too keep with the thought of "efficiency" to spend extra money for power capabilities that you do not need is inefficient all in of itself
also, my apologies for the semi-hijack due to PSU discussions.