My first guess would be that it’s not a network issue but rather a hard drive issue. Try running several streams from several machines to several machines. For Example
SourceServer1 -> DestinationServer1
SoruceServer2 -> DestinationServer2
If you use 4 or 5 sets of servers you will probably get your full 100 Meg connection. In order to sustain read and write throughput above about 20-30 mb/s on a single server you’ll need to have a very high end RAID array to handle the data.