Thin fins is ofcause the best because you get a larger surface area. The larger surface area gives a larger diffusion of heat from the hot material to the air. This is also the reason why it's good to have hsf, because you move the hot air away from the fins.
Hey - on that cooler - what spec will it run? What is your CPU running at and at what temp?
I really like the idea of the 3100(G?) not sure about the G but I've a feeling that my 1.6G Athlon may be too much for it?
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I have a 1000 (200) Athlon (AXIA), running @ 1460. The temp is 45-46 C, when running at full load. I used ACII and have 2 casefans + the one blowing directly on the cooler. The case is open. I havend crossed the L1 bridges yet, and I have the voltage on default. The good thing about the cooler is it makes the PC more silent too. If you wan't better colling, just get a faster fan.... My fan has 2400 rpm and 28,3 dBa.