For instance, upgradeability- I will want to be able to replace the CPU in a couple years, so I need one that will allow me to have that option.
Wow! It's almost impossible to buy a system that will last that long. The only way to get upgradability in today's CPU market is to get the slowest CPU a motherboard support. But it's not a good thing to do. Because usually for only a few more dollars you get a better CPU.
Both Intel and AMD will get new socket out within a couple of months. Basically no have have an advantage. Maybe Intel, because some actual motherboard will support Prescott CPU (if they ever come out...). But, by the time you will want to upgrade, PCI-X will be out and the TOP CPU will only work on new motherboard.
If I were you, I would wait a couple of month or buy now medium to high end system that will last long enough.
Athlon XP based PC have the advantage to be cheap and quite mature. nForce 2 motherboards are very well designed and very stable. But, this platform is nearly dead. We will probably not see any new XP chip. So If you buy a Barton 2500+ with DDR400 ram you will be able to overclock if to 3200+. But you will not be able to upgrade your system in the future. You will have reach the limit of the platform.
Actuel Intel P4C with Prescott ready motherboards are not bad choice too. They cost more than Athlon XP systems, but they might support some Prescott chip. Be cautious, because we haven't seen any actuel performance rating for Prescott on actual motherboard and maybe HIGH speed Prescott will not be support on the actuel Prescott ready board, because of power needed or heat produced. So, it's a double-edge sword. You pay more, you get some upgradability.
Actual Athlon 64 systems have 2 probems. They are as mature as P4C and XP platforms and AMD will limit this platform to 3700+. So, you can buy today an AMD 64 3000+ chip with a good VIA based motherboard (most reviewer's confirm that is the best A64 chipset on the market for now) at a decent price. But you will not get room for more than a 3700+ chip. On the other hand, the A64 are ready for Windows 64 bits. When it will be out, you would get a "free" performance boost. It will not double your system performance, but you might get 10% to 15% boost in general. And maybe some apps. will get a bigger boost.
Of course, all the actual MB don't support PCI-X (that will replace AGP). But I don't think it's real problem, because Video Card maker will still make AGP Video Card.
For me, if I had to upgrade today, I would get an Athlon 64 3000+ with a VIA based motherboard and DDR400 memory.
But, If I had to upgrade within a few months, I would wait to see the performance of new Intel and AMD socket/cpu. About March/April.
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