The real world power savings is very minimal, because unless there was a heavy load on the CPU, the two uses about the same amount of power. What differs is when there's a heavier load on the CPU, where the T is capped at a lower speed, thus having a lower TDP. The only time you really want to have the lower TDP is if you are trying to build a system using a really low wattage PSU, like a 60W or so, where the normal 2100 + drives might possibly stress the PSU.
I am running a 120W pico PSU.