I'll be adding some notes as I make while editing this episode. Thist first note also relates to recent comments about natural and necessary desires and how one of the key aspects of the unnatural / unnecessary category is that they CANNOT be satisfied.
I probably did not emphasize the "limit" issue enough in comparing PD3 to what Cicero is saying. I think there's definitely a parallel between PD3 and what Torquatus says:
QuotePD03. The limit of quantity in pleasures is the removal of all that is painful. Wherever pleasure is present, as long as it is there, there is neither pain of body, nor of mind, nor of both at once.
Torquatus in On Ends Part 1 - XII. Again, the truth that pleasure is the supreme good can be most easily apprehended from the following consideration. (3) Let us imagine an individual in the enjoyment of pleasures great, numerous and constant, both mental and bodily, with no pain to thwart or threaten them; I ask what circumstances can we describe as more excellent than these or more desirable? A man whose circumstances are such must needs possess, as well as other things, a robust mind subject to no fear of death or pain, because (2) death is apart from sensation, and (4) pain when lasting is usually slight, when oppressive is of short duration, so that its temporariness reconciles us to its intensity, and its slightness to its continuance. When in addition we suppose that such a man is (1) in no awe of the influence of the gods, and does not allow his past pleasures to slip away, but takes delight in constantly recalling them, what circumstance is it possible to add to these, to make his condition better?
Both of these underlined sections from Torquatus are making the point that after you reach the desired status then it cannot be made "better" or "more excellent."
As I think about it now that's probably the best way to understand the "limit of quantity" reference in PD03, and how it relatest to the "variety" issue. Certainly longer time allows for more pleasure in terms of time, and someone could argue that more time allows for more "quantity" of pleasure.
The ultimate point seems to be that the definition of the "best" feeling of pleasure is when pleasure is not accompanied by any pain. That fits nicely with the additional point no extra amount of time allows for pleasure that is "better" or "more excellent" than the pleasure we can experience here and now. And it's a target or a theoretical goal as much as anything else, because we can still be "happy" even if we don't always or even ever reach the point of eliminating all pain. As evidence for that we have Epicurus saying that he happy even during his final sickness and Diogenes Laertius and Cicero saying that Epicurus held that the wise man can be "happy" even under torture.
if indeed this is Torquatus' way of expressing PD03, and I think it probably is, then I'd say that this is a much more understandable-to-modern-ears way of saying it.