You are right about those memory issue, but I don't think this would change the results a lot.
First, the A64 architecture scales well, so it's easy to predict CPU performance. Second, the A64 2800+ is the entry-level A64, there is no "top-performer" crown to win there.
I think AMD just nearly killed the Athlon XP line with this CPU. Because the new A64 2800+ equal the XP-3200+ in most benchmarks. So, the only reason to buy Athlon XP system now is Duron, low-priced XP (1600+/1800+), or the Athlon XP-M 2400+/2500+/2600+ for overclocker's out there. People who want mid-range system will be better server with the A64 platform now that there is a truly affordable A64 processor on the market.
It would be very useless for anyone to buy a Athlon XP based system rated over 2500+/2800+, because you mostly can't upgrade it and the price difference with A64 based system is not much.
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Would you buy a potato powered chipset?