Silly question

[Vincent <10.50%free.fr@localhost>]

Dear gurus ;)

Just a silly question. If I understand well, any Intel Core 2 processor 
can execute both I386 and AMD64 kernels. Right?

If true, what are the benefits (and drawbacks) of using AMD64 instead of 
I386? Increased memory space, but is there any performance upgrade?

Thanks for any (not too silly) answer to that naive question.

Vincent