Note that on a high-speed network it takes less time to transfer 1 Terabyte of data than one might expect. It is usually sub-optimal to try and get 900 megabits per second of throughput on a 1 gigabit per second network path in order to move one or two terabytes of data per day. The disk subsystem can also be a bottleneck - simple storage systems often have trouble filling a 1 gigabit per second pipe.
In general it is not a good idea to try to completely saturate the network, as you will likely end up causing problems for both yourself and others trying to use the same link. A good rule of thumb is that for periodic transfers it should be straightforward to get throughput equivalent to 1/4 to 1/3 of a shared path that has nominal background load.
For example, if you know your receiving host is connected to 1 Gbps Ethernet, then a target of speed of 150-200 Mbps is reasonable. You can adjust the number of parallel streams (as described on the tools page) that you are using to achieve this. If there is a T3 (45 Mbps) link in the middle of your path, then your target speed should be no more than 10 Mbps. However most DOE labs and large universities are connected at speeds of at least 1 Gbps, and most LANs are at least 100 Mbps, so if you don't get at least 20 Mbps, there may be a problem that needs to be addressed.