Although I agree generally that DDR is not worth it on P3, I still think a few points can be made.
The P3 CPU FSB runs at 133, and the memory bus on a DDR board is 266 (effectively), so you would assume that extra 133 is wasted. But remember, this happens via the chipset's memory controller, and the CPU is NOT the only thing in the system that directly accesses memory. There are a number of devices that use DMA access to the memory, so any time more than one device wants to read/write from the memory, they must wait for the memory controller to become free. Therefore the faster the memory bus is running, the faster the other device gets access to the memory.
Of course, realistically only the CPU is reading/writing large amounts of data to the memory, but the fact that other devices jump in and interfere occasionally can affect performance. The main one to remember is your AGP video card, any game that uses a lot of large textures that can't be stored directly can use the AGP's ability to operate directly on the system memory.
Another point is the chipset's DDR implementation. Remember when DDR first became available for Athlon systems, say the KT266? Everybody was disappointed with the improvement in performance it offered. It wasn't until the KT266A (or before it, SIS735 or even AMD760) that we saw performance improvements as expected. It seems safe to say the same applies for the P3 DDR chipsets. Although you can check
here to see that there is some performance gain to be had with DDR, at least on dual CPU setups.
As some extra info, there is a (p)review of the IWill DVDu266-RN that uses the new Apollo Pro 266T chipset that posts some nice benchmarks
here. Oldfart you mention Sisoft memory benchmarks of 532/519, is that at the CPU's normal 1266/133fsb, or at your overclocked 1444/152fsb? Even on a 1133/133fsb this board scores 556/582.. perhaps we have the improved memory performance on the 266T chipset that was previously lacking.
But in all, besides my extended ranting, I do agree that the 133FSB of P3 seriously limits the advantage of DDR memory, not worth the extra money unless you want that extra few percent at any cost. My main reason is limited options.. can anyone suggest ANY other dual Tualatin board not designed for the server market?