Comparing the 2 is an apples-to-oranges venture.
The Whisper was originally designed for military/law enforcement applications (240 grainer at around 1040 fps) but found another life as a mid-range deer round -- and it performs much like the .30 Herrett. In other words, feed it the 125 grain BT and you have yourself an honest 150 yard deer-dropper, even from a 10" tube.
In that arena, no, it is not a low-pressure round and is run full-throttle in the Contender. It pales in comparison to the .308 WCF when ballistics of both are put on paper but is perfectly suited to its intended tasks.
Also, if you want to try the sub-sonic game, you need a fast twist (1:8 or 1:7) to shoot the 240 grainers, which means a TC factory tube will not suffice.