I do not think dragon bolts are worth it for anything but cas at the moment
say you spend like 10 of them per kill
that is 10x5k or 50k
say you average kill is worth 200k
you are paying like a 25% tax to save what 10-20 seconds?
if paying 25k to save 10 seconds is worth it you have to be earning like 9m or more per hour
whisperer is mage so the 70m wont save you there