samba - May 2006 - PDC BDC logon server

If I have a PDC and 3 BDCs on separate networks, with no clients
on either of these networks, should the BDCs still be the preferred
logon servers or do the have to be on the same network segment?

Does where the wins server is (on the PDC) make a difference to
which responds first?  I've got 95% of my clients using the PDC and
would like to spread the load a little.

Samba 3.0.21c on Solaris 10

Ideas?
        Duncan