I am not using a local folder for e-mail in the form of .pst. I am using the
Mailbox on my exchange 2003 server, but I do have a .ost file for working
offline of course.

My .ost file is 1 GB in size.

But why should this be the reason for my Outlook 2007 to be this much slower
than my Outlook 2003 given identical factors on both machines, with the
exception of noted hardware changes?

Is Microsoft mandating that everyone use smaller Personal Folders/Mailboxes
in order to make Outlook 2007 perform as well as Outlook 2003?