The Latency - How to Calculate Bandwidth Throughput
Latency decreases the total amount of bandwidth one singe TCP stream can use. The more latency, the lower the bandwidth. TCP Window Size also affects throughput.
Brad Hedlund has created a very good article with specific calculations.
The biggest misconception I hear is that the network is limiting Windows to 10Mbps when transferring files over a 100M WAN connection. One TCP Stream can only consume so much bandwidth depending on Window Size and Latency. Use a tool such as iPerf can test link throughput by pushing UDP packets that don't rely on TCP Window Sizing and latency.