^^ EMUs really don't have much a higher speed than Go's current diesel locomotives. The increase in "speed" is going to be coming from the faster acceleration and stop/start times.
With the current locomotives, adding a few new stations on most of the lines mean the trains won't even be able to get up to their top speed between stations, which means everything goes a lot slower. With EMUs, they'd easily be able to reach their top speed much faster, which means a faster average speed.
The more stops and slow downs you have, the more the benefits of Multiple Unit and Electric trains become visible. Right now, trains take like three or four kilometers to reach their top speed. An EMU might be able to reach top speed in like half a kilometer, which means they go much faster. Basically, an extra station or two with the current trains are killer, but are a lot more manageable with EMUs.