Check this homemade WB out

[NaeKuh]

Mass and surface area are very key.

Ideally you want the least mass and most surface area at the base, and most mass and further surface area everywhere else on the block. If you get the base right, the rest of the block is just icing on the cake. This hybrid idea could actually work quite well if you have a base type array on the topside of the block. It would hurt flow though.

Errrr your thinking is half correct... so i give you half credit.

Mass is not important in relation to efficiency of medium which is used to pick up in relation to surface area.

In water, where you have a greater absorbtion on the water side vs disappation of heat on the air side, you want as little mass on the copper as possible, and more surface area so water can pick up.

If you have more mass where water picks up or disappates, you have excess.
This excess is usless in a ambient system, because of the difference in mediums.

Now in a Chilled environment mass is important.
Why? because your not sheding heat which an ambient system does, you are pounding cold.

So you want MASS, to keep the block Cold....

Anyhow Nate i was talking to vapor, and we both said it would be interesting if you threw a TEC in between the fins and that top plate.
If you had something to pull sub ambient, and the fins cooling the hotside on the tec you might have an interesting product.

Because if i calculate correctly, you can probably throw a 60-90W tec on a 12V power rail without much problems.
Then you will have 45-65W of cooling on your CPU component, and your rad can shed the excess heat off.

You will lose effiency in your system, however you would get some interesting results... especially on a long idle period followed by quick load sessions.... because your prechilling the block each prefront load with that MASS.

You wont pull sub ambient because your rad would turn into a heater if your water went below ambient.
But you would pull work off your rad, and probably get closer to ambient.