The updates to SEP clients are only 60mb in the case when the clients definitions are further out of date than the versions that the SEP Manager has stored.
If you set your retention levels correctly this should only happen in very rare occassions.
Normal incremental updates should be no more than 100-200K to each SEP client per day.
You should also use Group Update Providers (GUP) at each remote site as it will save bandwidth.
When a SEP client requests the definition update it is sent to the GUP which then caches it for all future requests of the same definition.
cheers
Z