If your network connection is limited to 100Mbps, your Network Card configuration in SolusVM is probably set to Realtek 8139. Please use the Intel PRO/1000 or Virtio network card setting to be able to use all of your 1Gbps connection.
Additionally please append the following lines to the /etc/sysctl.conf file:
net.core.rmem_max=16777216 net.core.wmem_max=16777216 net.ipv4.tcp_rmem=4096 87380 16777216 net.ipv4.tcp_wmem=4096 65536 16777216
After saving the file, type sysctl -p for the changes to take effect.