Since my rad starts leaking about 6 month ago I`ve been using the exact "no bucks, no noise" solution you asked for; Just a five gallon water bucket with the pump suspended inside.
My cpu is a duron 1000 @ 1400 1.9V. when I turn it on the water temp start rising about 2.5ºC/hour, until it stabilices arround 30. The highest I`ve ever seen was 32, in a floating "analog" termometer I have in there.
This "miracle" is only the combined job between natural convection, radiation and evaporation. Every week I need to refill about two quarts of water. In part I`m lucky to live in a dry climate. If that`s not your case your stable temp should be higher, but not to much, because convection and radiation become more efficient as temp difference with ambient increases.
I`m sure this is not an elegant solution, and sure that with a decent heatercore I could overclock more, but I`m used to the low noise; Now my ps fan at 6v is driving me crazy!
