best way to upgrade from mysql4+PHP4 to mysql 41+PHP5

[ml at sd2i.com]

We want to upgrade some 4.11 boxes from mysql4+PHP4 to mysql 41+PHP5 
with about no interruption as there's many users

I want to know if i have another faster solution than what i plan to do, 
i mean :

pkg_delete php4*
pkg_delete mysql*
then install php5 and mysql from port

we have many dependencies on mysql-client (mydns, postfix, pureftpd, 
etc.), do i need to reinstall everything against the new mysql client 
version ?

i thought about force reinstall without removing old versions, but how 
can i unregister the packages without removing the files so the server 
will continue to run during the compilation step ?

finally, how can i know the incidence on mysql databases, i already read 
the official mysql 4.0=>4.1 howto, but maybe using the ports installer 
implie other stuff to do ?

thanks for any help.