A GUP does not imply SEPM has more work to do, a GUP will relieve SEPM from occupying itself with providing Def updates to SEP clients.
As for replication; keep in mind that you need a considerable amount of bandwidth, if you're thinking about setting up a SEPM server at multiple sites (fairly small, let's say about 1000 clients), think about a GUP (for example a print server) or LiveUpdate Administrator where the can obtain updates from.
Best of luck!
Dries