Potential downtime during MSI upgrade

I'm considering deploying websites to an Win2k3/IIS6 machine using a MSI built with WiX.

The website in question has a collection of .html, .jpg, .js, .swf & .asp files (no ASP.NET)

I'm doing a "Major Upgrade" when installing the MSI (i.e, it first uninstalls the old MSI, then installs the new MSI). This is the only way I can figure to get the MSI to remove redundant files.

My question is; will there be any downtime for visitors to the site during the uninstall / reinstall process?

Or does IIS cache the files being used by currently open connections?

From stackoverflow

• No, you'll definitely be in an outage. It does not cache that info.

• If you're that concerned about downtime, you should be thinking about load balancing and redundant webservers.