This morning I went to try out the new circle line. I was trying to see whether it help to cut down travel time from east to north. The route chosen was from Bedok to Yishun.
You can take train to Paya Lebar, transfer to circle line, alight at Bishan, subsequently transfer to North South line. The result is not surprising. After taken into account of walking and waiting time during two transfer, it doesn't really cut down the time.
If you take East West line and change at City Hall interchange, the time required would be
Train - 16min
Waiting - 5min
Train - 28min
= 49min
If you take the circle line,
Train - 6min
Walking & waiting - 8min
Train - 13min
Walking & waiting - 8min
Train - 12min
= 47min
You can only save 2min of time