Okay, let's see...
Thermal pads are garbage. They're invented to keep the cpu so hot that the average joe can't overclock his cpu, because it'd just go unstable and crappy. Arctic Silver 3 is good, and not too expensive, so it can cut off a couple of degrees from your temp. The rating of a fan just means that it'll keep a cpu of that speed cool enough to function properly, so it doesn't really say much regarding how well it performs. The 2400+ t-bred is a good cpu, because it has been known to overclock quite well (check out http://www.overclockers.com's cpu database for some examples). Bartons have more L1 cache, so they're more efficient than t-breds when run at the same clock frequency, and they have also been known to overclock nicely. Before you get a barton you should at least check whether your motherboard supports them, or if a bios flash will do the trick.

Since you probably want to overclock more than just a grain then you'll need a good heatsink / fan combo. The Thermalright SLK-800 and SLK-900 sinks are great, but not every motherboard has room for the SLK-900, since capacitors are in the way. Panaflo and Papst fans are good if you want a decent chunk of CFM (cubic feet of air moved pr minute by the fan), but if you want to get REALLY good results then you'll need to go for Delta fans. Deltas are extremely loud (the 80mm fan is rated at 52dB), so some use them only to overclock all they can, and then switch back to a quieter fan when they've run 3dmark at the overclocked speed they reached.

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