In your case, bigger is not always better, a large zalman will not suit you well with out help. The large copper heat sinks with slow fans work great in normal situations, they balance out the spikes of heat by spreading the heat over a large area, and then slowly cooling it down with a large, slow fan. In your case, you are trying to cool your heat sink with hot air, so you will need much more air to cool it with, not more copper. If your not concerned about noise, get a large box fan, and mount it on the side of your case, and suck the air out, better yet, if both sides come off of your case, blow in one and out the other.
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