well let me start saying that it's to soon to buy a 64bit processor (there still isn't a proper OS!! and in consecuence there aren't 64bit programs that use this technology). maybe in 3/4 years, think in a future update, and then those processors will be 3/4 times faster.
and now intel or amd?? my guess: amd and i will explain why
intel has the most powerfuls processors that's for sure, specially in multimedia benchmarcking, the problem it's that comparing quality/price they loss for a lot. the processor is expensive and more expensive it's a MoBo with intel chipset.
amd has slower processors but they are very cheap and MoBos are cheaper too. their processors are hot like hell but expend some cash in a good fan or liquid cooling and problem solved, both still cost less than a p4.
in this part i will answer, what chipset??? well another time expend a few $/€ and buy a nforce2 based chipset. why?? because they have the hability to lock some frecuencys, take up some voltages... (talking about overclocking). in conclusion AMD+nForce2 will be cheaper than a P4+Intel but will be less powerful...
for the pci-e, amd is not thinking in it now, as in ddr2 or similar things. for now this is not too important because benchmarcking on pci-e and ddr2 are not giving a critical perfomance increment.
finally, taking up AMD vs P4. i will choose particular hardware: 3000+/3200+ and A7N8X/-E /Deluxe. look for caracteristics of them and choose the one you like. overclock your cpu frecuency 0,2/0,3ghz and it will faster than a new p4. aren't you sure?? check down my hardware and check
here the results, my current system it's faster than a 3.2ghz p4 extreme edition.
hope this solve you some of your problems and answer some of your questions. if you think i'm wrong on any point please let me know