I have a windows server running 2012 r2 and single connection upload limit seems to be around 10-20mbps however using something like downthemall I can max out my home connection using the segmented download feature. Below is the tcp parameters.
TCP Global Parameters
----------------------------------------------
Receive-Side Scaling State : enabled
Chimney Offload State : disabled
NetDMA State : disabled
Direct Cache Access (DCA) : disabled
Receive Window Auto-Tuning Level : normal
Add-On Congestion Control Provider : ctcp
ECN Capability : enabled
RFC 1323 Timestamps : disabled
Initial RTO : 3000
Receive Segment Coalescing State : enabled
Non Sack Rtt Resiliency : disabled
Max SYN Retransmissions : 2
I have tried various configurations and even gone so far as to force ctcp being enabled via registry editing but so far have not had much luck.