IMS of Exchange 5.5 migrated to SMTP of Exchange 2000

Hi there,

I have a design discussion of migration IMS to SMTP in Exchange 2000.

Here is the scenario:

There is a mixed mode of Exchange 5.5 and Exchange 2000 with 4 sites.
Central site is the largest one. IMS of 5.5 in Central site is for
enterprise Internet mail . IMS is also routing other 20 external domains.
There are two designs of how to migrate IMS to SMTP connector.

Common: create 20 new receipts policies to match each external domain SMTP
space.
Design 1:
(1) create a new routing group under central administrative group.Now there
are two routing groups in the central administrative group: one is from
existing Exchange 5.5 central site, the new one is dedicated routing group
called Internet Gateway with two members/servers.
(2) created 4 routing group connectors for the 4 sites/RGs
(3) created 20 SMTP connectors for each no-authoritative domain, address
space: exteranldomain.com cost 1, configure to forward to IP address of
external smart host
(4) create one Internet SMTP connector with address space * with highest
cost
(5) all SMTP RGCs configured for enterprise and with two bridgehead servers.

Design 2:

(1) In the existing central routing group, create two SMTP connectors with
same address space and cost, like * and 1; configure to forward to internal
UNIX smart host.
(2) Each SMTP connector has only one bridgehead server.

I would like to have your opinions and experience here.

Thanks you very much in advance,

Wensi