The Pentium 4 has been shown to perform very well with DDR RAM, beginning with VIA's 'illegitemate' efforts and the P4X266 chipset. Now there are plenty of P4+DDR solutions available, combinations which don't suck as some people would have you believe. However Rambus still provides greater memory bandwidth than current DDR solutions (especially with the release of PC1066 RDRAM) though at the expense of having higher latency. To put it simply, the P4 loves lots of bandwidth, which DDR is now able to provide.
Comments about the P4 being slower than an Athlon in everything are somewhat exaggerated. Take Lightwave for example, the performance boost whilst using a P3/P4 system is quite substantual (and before someone mentions SSE, remember that Athlons also have SSE instructions). For professional work i.e. not games the P4 is quite a good performer.
Now for the downsides. P4's are somewhat more expensive than equivalent AMD solutions, however there have been times where P4's have retailed cheaper than Athlons Mhz-Mhz. Their lack of performance Mhz-Mhz compared to other CPU's is legendary, partly due to a hyper-extended (not official terminology) pipeline which hasn't worked as well as in theory
With that P5A, chances are that it will support up to K6/II/III-550, which is still a far cry from a decent system nowadays. Turn it into a server of some description and go buy a Duron+DDR system
