I was playing DRS a few days ago when I thought about something. The maximum speed limit on both mainlines is actually 90mph however at this speed your target speed is always 70mph . I think that the target speed should be based on what the actual line speed limit is rather than on how fast the train can go since the train can overexceed its maximum speed.
I respectfully disagree :) In real-life you can exceed the line speed limit at the risk of derailing or damaging equipment. You can also exceed the train's designated maximum speed at the risk of derailing or damaging the train. You shouldn't do either though. In the case of the 1st gen DMUs the max safe speed is probably limited by the power train, but for safety reasons, many other trains have lower max speeds than what they could actually reach.