I *think* the (my) problem with outlook is that it off-loads searching and indexing to the exchange server. Consequently, with a good exchange server outlook works great.
With a fake exchange server (Kerio) or a simple IMAP server (SME), I find that if I start an email search in Outlook I can open Thunderbird, let it download the last week's worth of email, search, and find an obscure email from 6 years ago before Outlook finishes.