First you must switch to RGB, if you have DPP 4 the easy way is under the "Adjustment" menu item and then "Color work space" and go to wide or RGB gamut. you can jump back and forth - the jump to RGB is "hmm that neat" the jump back to sRGB is "ooof that is flat"

As to the value of calibration I will leave that to others. This was fun enough for me.