Using BDD to deploy Vista and Office 2007...

Assuming that you have recent hardware platforms (3.2Ghz and 7200RPM drives)
and decent networking (100MB), what are your best guesses at how long an
installation should take (at the client's PC). I've watched a couple of
webcasts on BDD and asked the same question. Their reply was "with a minimal
OS, about 30-40 minutes". This seems a little excessive. We are currently
deploying WinXP-SP2 with Office 2003 and several smaller apps in under 30
minutes using Ghost DVDs. Our developer image also has VS, Visio, Project,
and several other med sized apps and only takes 40-45 mins. I'm concerned
that BDD may be faster for me to setup, modify and manage, but it sounds like
it will be considerably slower to deploy in the offices. The time it takes to
deploy in the offices is crucial. At our current rate, we deploy about 70 PCs
per day for 3 months to 4000 clients. I'm concerned that if we used the BDD
method, it would drop us down to about 50 per day and extend our deployment
time another month.
What are your comments on this?