Well the first block was built with a heatsink with shorter fins than the new one. Can't really say much cause the first block was also in a the first watercooler setup. When I went with the FREAKISHLY larger K6 heatsink(which was cut down to fit in a 4" PVC Cap), I couldn't really tell ya any performence difference. But I can tell you that the heatsink itself did 82F idle while the waterblock can do 77F idle. Now I did see a waterblock with small raised bumps on the inside of it. This may do a good job, the thing is, using a heatsink just forces the water everywhere, while a block you buy(standard ones) are channeled, now having small fins in the channeled ones would proably work well.
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Watercooled K6-2 450 at 600