Although processor makers probably hate us for saying so, the processor actually plays a relatively minor role in overall system performance. The difference in absolute processor performance between a $50 processor and a $500 processor may be a factor of two or less. Nor does buying a $500 processor make your system run twice as fast because processor speed is only one element of system performance. Before you plunk down $500 for a processor, consider instead spending that extra money on more memory, a faster video card, a SCSI hard drive, or all of those.
AMD Athlon XP. In this price range, spend $75 or so on the processor. We recommend choosing the least-expensive Athlon XP you can find in retail-boxed form. Low-end Athlon processors provide incredible bang for the-buck. Your system won't be quite as fast as one that uses a midrange or faster Athlon XP or Pentium 4, but it won't be all that much slower, either.
Intel Pentium 4 or AMD Athlon XP. In this price range, you have a bit more room to play, and it makes sense to allocate some of that extra money to a faster processor. At the lower end of this price range, choose the fastest retail-boxed AMD Athlon XP you can find for $100 or so (the Intel Pentium 4 doesn't compete in the $100 price range). At the higher end, choose the fastest retail-boxed Intel Northwood-core Pentium 4 or AMD Athlon XP you can find for $150.
Intel Pentium 4 or AMD Athlon XP. This budget level provides considerably more options. For a system in this price range, choose the fastest retail-boxed AMD Athlon XP or Intel Pentium 4 (533 or 800 MHz FSB) you can find in the sub-$200 range.
AMD Athlon MP. If you run Windows 2000/XP, Linux, or another SMP-capable operating system, we recommend using a dual-processor system. In our experience, responsiveness in a multitasking environment is better with two midrange processors than with one fast processor. If you choose components carefully, you can build a dual-processor Athlon system for only $250 or so more than the cost of a comparable mainstream system. Your system won't run any one task as fast as it would with a faster single processor, but it won't bog down when you're running many tasks, as the fast single-processor system will.
TaiSol or DynaTron. A retail-boxed processor includes a heatsink/fan unit that is perfectly adequate for routine use. If you buy an OEM processor, which does not include a heatsink/fan unit, or if you overclock or otherwise push your system beyond its design limits, you'll need a high-quality third-party heatsink/fan unit. Such units vary widely in price, cooling efficiency, and noise level, but the best units overall in our opinion are those manufactured by TaiSol and DynaTron. We have used various TaiSol and DynaTron heatsink/fan models on various processors?including Celerons, Pentium IIIs, Pentium 4s, Athlons, and Durons running at various speeds?and have found them to be effective, quiet, and reasonably priced.
We constantly test and review processors. For information about which specific processors we recommend by brand and model, visit http://www.hardwareguys.com/picks/processors.html. We also maintain a set of system guides that detail our currently recommended system configurations for various purposes and in various price ranges. You can view the latest system guides at http://www.hardwareguys.com/guides/guides.html.