Run with the 1 master/primary (default, only way) and make them all parent servers.
Then allow the clients to seek any parent server, don't assign, use roaming and use (been a while, forgive me!) the option that allows the client to use the parent that responds first, or even load balancing. This will spread the clients among the 3 parent servers.
They won't all update at the same time that way - it will vary. And if the clients are online most of the time, they will be fairly current and will get only the deltas anyway. Only if they have been offline a while will they need more - or the full definitions.
SAV's update methods are VERY effecient! When I was at PFG, the network team insisted on "sniffing" ALL apps that touched any desktop or notebook image. SAV was tested and found to be among the least intrusive of any app that used the network. they couldn't believe how, for the amount of "apparent traffic" it looked like was going, how little load was actually placed on the network.
But using all 3 servers as parents (running SAV server version on them) and using roaming with load balancing, etc. - the load will be spread, clients will get updates spread out and not all at once.
SAV 7.5 through 10.xx were very effecient, IMO, at network traffic and there were many good tools, roaming among my favorite!