Quantum stockpiles help quite a bit at times, and other times you'll see virtually no benefit.
Although they are simple to set up so might as well use them. Actually if you spend some time and set up a moderatly efficient minecart hauling system in your fort, it eats up a lot of the pathfinding time (since when pathfinding for a minecart, they only search down rails, so it gets real fast) And usually I find that most pathfinding comes from dwarves hauling stuff from different floors. Woodcutters can be a bit problematic, but thats as simple as not cutting wood. Also theres always putting a "low traffic" or "restricted" around your fort entrance to keep from wasting too much time pathing there.
Also, 1 thing that I've figured out with more recent play. Most of my early forts were based around a + of corridors (with the whitespace filled with stockpiles and workshops and such)
Instead I build them around 1 5 wide (with 2 rail lines) corridor with the working spaces to the north and south. With the "doorways" to the working spaces all set as low traffic because of the rails. Everyone prioritizes pathing horizontally down the wide hallway first, then heads north or south into their necessary workshop or stockpile. The center of the hall is numerous quantum stockpiles that are set up to feed materials to the nearest workshop. (Most workshops are in a 5x5 room, workshop centered, and the remaining spaces are an output stockpile for products)
On my laptop, this lets me keep a fort running (ver 34) with up to 250 dwarves before I start getting worse slowdowns. (At that point, I start having issues though, really need faster RAM on this thing, the processor is fast enough, the RAM is definitely my bottleneck on here)