Word on the street (the seedy back alley archives of the internet : ) has it that the thinner finned heatsink is the better one, almost as good as the copper one used with the 1.42 DP. Apple very specifically says both are "equivalent" in their service documentation. From what I have seen the thin finned one is less common.

Regarding the CPU's, they might both be dual 1.25 but there were at least two versions - 1MB cache per processor (7455b) and 2MB cache per processor (7455a). There may also be a difference in the cache:CPU clock ratio. The 1.25/1MB processor was the later version and uses 7455b which should be able to run at a lower voltage (less heat) and possibly overclock higher.