Are there performance advantages in storing bulky field in separate table?

Hi all,
I'm designing a Postgresql database, and would appreciate this design advice.

I've got a fairly straightforward table that's similar to a blog table
(entryId, date, title, author, etc). There is, however, the
requirement to allow a single, fairly bulky binary attachment to
around 1% of the rows.

There will be a few million rows, and I value efficient searches by
date, title, and author.

Would there be a performance advantage in storing the attachment in a
separate table - linked by entryId foreign key? Or shall I just
include it as an ALLOW NULL field my blog table?

[of course, I'd appreciate redirection to the 'right' list if this is
the wrong one].

cheers,
Ian