i386 vs x86_64 on a Xeon EM64T

[Richard Lefebvre]

I'm trying to figure out which binaries I should install on a dual
processor Xeon EM64T with 4 Gig Ram total (the memory won't be upgraded
for a long while). I tried booting both FC3 disk1 and they both worked,
but the x84_64 was much slower booting and starting X. Will the slow
down be general, or once fully installed everything will be just as
fast. What would be the big advantage of using x86_64 over the i386?

Richard