I'm wondering whether we need to. If the Epicurean life is guided by the pursuit of pleasure, there is no hierarchy of pleasure, and the limit of pleasure is the removal of all pain and fear, then intensity and duration of pleasure are meaningless, practically speaking. They are useful only as rhetorical tools as in PD3 and PD9.
In other words, as long as you are pursuing a life of pleasure, what is most pleasant doesn't matter. And it can't be measured in either intensity or duration. This is why Epicurus could have such pleasure as he was dying in agony: he was still pursuing pleasure, and the pleasure of his thoughts was driving out the pain of his strangury. Similarly for a sage on the rack.
A life of pleasure is pursued moment by moment. So wouldn't the proper measurement be the feeling of pleasure in each moment? That would be duration. Wouldn't the greatest intensity then be the lack of any pain in that moment?