You see, maybe you don't realize it, but you're arguing that "your system" is better than the current system... because its units are some arbitrary, undefined smaller unit!
THEN, you argue "your system" is better than mine... because the units are some arbitrary, undefined LARGER unit!
The whole argument you are making is that I'm somehow asking for the game to measure down to the picometer, and then offer your idea up as a Golden Mean between these two "negative extremes".
OK, so I'm officially confused.
Aren't you proposing representing everything by the smallest possible unit of volume? If you're not, then what
do you propose? If you've written it already I must have missed it, in that case we've been wasting a lot of time here...
I am indeed proposing something smaller than the current units (which are quite arbitrary - a log is "the amount you get from 'a' tree", a stone is... well, just arbitrary).
The units I'm proposing are arbitrary only in the sense that they could be picked within a range - a "plank" could be anything from a big fat near-beam to a relatively short and thin piece of wood - but it couldn't be
any size. Toady would pick some average size that corresponds well with most people's idea of a "plank", and also allows all furniture/construction to be done reasonably with whole numbers of them. And so on for other types.
A prototypical plank, in other words. Doesn't exist in reality, but approximates well what does exists in reality - better than the current wood logs do, certainly - and provides
sufficient detail for that which they're used for.
Now then, let's look at the way that the game actually works. Dwarves will prefer (potentially very heavily) to stack items of the same sort if they can at all help it. With fungible piles of wood, this means that they will continue putting every single scrap of wood they can find into one pile until the pile hits whatever it's arbitrary "full" size is, at which point, they start up the next pile, probably directly next to the first. When some wood needs to be added to the pile, they place it in the partially-full tiles first. When wood is taken from the pile, they go to whichever is closest first, which is probably the same tile they took from last time, which cleans up those fractions leftover if there were any rather nicely before they move on to the next pile.
In the above I was assuming that a dwarf will prefer to grab everything he needs in one pick, over starting with the nearest pile if that's insufficient. How does it work now? Is there any facility for "grabbing enough" material for, say, melting metal - or is it just "get 1 metal thing, bring it back, see if it's sufficient, get 1 more metal thing..."? I confess I don't know. Both our systems needs to deal with this in a proper way, at least.
Anyway, if the stockpile is constantly being replenished as you postulate, the problem would indeed be mitigated. On the whole, the performance argument is not my main reason for preferring units of some tangible finite size rather than (as I've understood you) the smallest available unit. It's most of all about aesthetics. And there, I doubt either of us will be able to win the other over. It's not up to us to decide, anyway