Multicast performance isn’t really dependent on an awesome server - that’s part of the method. The server only sends one time and many receive.
Your problem is probably poor-quality network equipment you were using for multicast. Higher-end network equipment like Cisco Catalyst would not have these issues. The cheaper the network equipment, the worse multicast will be. It’s total-internal-throughput that matters. If you have an el-cheapo crap 10 dollar switch that is advertised as 1Gbps, it may only have 2 or 2.5Gbps total-internal-throughput. The max it can transmit in and out of all ports simultaneously at any one time. To truly take advantage of multicast, if your 1Gbps switch has 8 ports, it needs 8Gpbs total-internal-throughput. If it’s a 48 port 1Gbps switch, then 48Gbps of total internal throughput.
Networking is the purview of campus IT. However I do know a few things. The closet next to my office has a few Cisco Catalyst 3500 series switches. One was replaced about 18 months ago when the fan quit working. The main switches on campus are connected with fiber optic cable. Everything else is cat5e. There may very well be cat 5 in the walls and coming out of the ethernet ports, but I don’t know for sure. Our work room has a netgear ProSafe GS108 in order to make 2 ports become 9. I also know our network has some sort of traffic shaping system, but whether or not that affects FOG I don’t know. The library public computers (including the FOG server) are on their own subnet with a restrictive ACL. The arrangement prevents our imaging server from interfering with the one campus IT uses. With the exception of the netgear, none of this sounds like poor quality equipment. My feeling is the issue is low quality or old cables combined with a low end server.