I haven't installed RU5 so I can't confirm but this is from the admin docs (the second bulleted item sounds very interesting):
Use multiple Group Update Providers when your network includes
any of the following scenarios:
■ You run the latest client software on the computers in your network
Multiple Group Update Providers are supported on the computers
that run the latest client software. Multiple Group Update Providers
are not supported by legacy clients. Legacy clients cannot get
content from multiple Group Update Providers. Legacy clients
cannot be designated as a Group Update Provider even if they meet
the criteria for multiple Group Update Providers.
You can create a separate LiveUpdate Settings Policy and configure
a single, static Group Update Provider for a group of legacy clients
■ You have multiple groups and want to use different Group Update
Providers for each group
You can use one policy that specifies rules for the election of
multiple Group Update Providers. If clients change locations, you
do not have to update the LiveUpdate Settings Policy. The
Symantec Endpoint Protection Manager combines multiple Group
Update Providers across sites and domains. It makes the list
available to all clients in all groups in your network.
■ Multiple Group Update Providers can function as a failover
mechanism. Multiple Group Update Providers ensure a higher
probability that at least one Group Update Provider is available in
each subnet.