A multi-cart system can be incredibly fast, limited only by how fast a roller can push carts off a single tile. You can pack enough carts into a well designed automatic system that you have 1 cart per every 2 tiles in the track or so, thus delivering a constant flow. The problem is that that's roughly 88 iron minecarts for you to make. But still, if you find it preferable, here's the design of my old exploity magma lifter from 34.11 - I say exploity because the main propulsion method is impulse ramps, but you could easily place normal ramps and run a column of gears down the centre with rollers on the tiles adjacent to the centre. In fact, that would make life easier at the bottom, as you wouldn't need to build a water reactor or anything down there to provide power. Anyway, here ya go:
The basics
ooooo
o^^oo
o..oo
o.ooo
ooooo
This is the actual shaft. Just rotate and repeat all the way down to the magma sea. The top left ramp is an impulse ramp connected to the north wall and ejecting east and the other ramp is a normal ramp connecting west-south, which leads up to the next layer's impulse ramp, and so on. The central open space is a shaft going all the way down to the filling station at the bottom.
At the top you have a receiving station like this:
++++T+
++++P+
ooooDo
oo.^^oo
o╔HoT#o
o╚══╝oo
oooooo
Now this does look a bit complicated I'll admit, but it's really not that bad. The topmost T is a track stop where dwarves push carts south - you can accomplish this by making a (h)auling (r)oute, with just the one (s)top on that track stop, set to push south immediately. Assign an iron minecart (v)ehicle to the route and then forbid it as soon as the dwarf pushes it. Assign another one and forbid it once it's pushed, and so on. The P is a pressure plate linked to the door that activates only for minecarts of any weight, but NOT citizens. The two ramps are impulse ramps to provide the incoming carts with the power to get round the little circuit. The bottom T is a track stop with minimum friction set to dump east. The # is a grate or hole or whatever where the magma goes. The H is a hatch linked to a nearby lever which will let you stop the system once it's going. The rest is just flat track, or impulse ramps if you're feeling dangerous - I say that because if you ever want to stop the system, the carts should come to a rest on that flat section, and if there are impulse ramps there, dwarves may be injured when they remove one cart from in front of another. The hatch opens onto the shaft I mentioned earlier, so that carts can simply free fall back down to the magma.
Advanced stopping of the minecarts
If you have space on the z-levels under your receiving station, you can remove the hatch on the main level and instead place it 2 levels below, like so:
ooooo
ooooo
o^Hoo
o^..o
ooooo
Because of a possible bug, minecarts falling and landing on top of another minecart will stack infinitely in the tile above the first minecart, so by placing the hatch two levels down, you can stack an unlimited amount of minecarts safely. This is very useful if you want 100 minecarts running simultaneously, but also want to be able to stop them at some point.
Now the filling station is the really tricky bit:
z+0
ooooo
MG^oo
oo^oo
ooooo
ooooo
z+1
ooooo
PG.^o
oo.oo
ooooo
The ramps on z+0 both have highest-speed rollers on them (rollers made from iron/steel chains and magma-safe mechanisms), and are both impulse ramps as well. They both connect north-east. The bootom roller pushes north and the top one pushes east. G represents gear assemblies, made of magma-proof mechanisms (obviously). M represents your magma source, in my case a pump pulling directly from the magma sea. If you build the pump so that its solid tile is where the M is in this diagram, it will be powered by the gear assemblies. P represents a connection to any power source you see fit, be it a conveniently placed water reactor or a 150z tall vertical axle connecting to your windmill farm. Finally the ramp on z+1 is an impulse ramp connected east-south, which will spit carts up the south path to connect to the rest of your elevator.
Put the three bits together and you have a very decent magma transport system which is WAY less work and requires WAY less power than an actual pump stack, even if it is a little bit slower. At the top, make sure any cistern you make for the magma is tall and thin rather than wide and shallow, because evaporation is hectic. Also, once you've filled the channels under your forges and smelters to 4/7 or more, you won't ever need to refill it because at that depth it won't evaporate and it's not actually used up by the forges/smelters.
Note that this entire design needs dwarves off the tracks. Dwarves on the tracks is guaranteed to equal disaster, because minecarts filled with magma are heavy and getting hit by one every three seconds is fairly lethal, so you should make sure any maintenance doors on the actual shaft are kept sealed when the thing is running, that all such doors are kept tightly closed with (o) as well as forbidden (because pets can still open forbidden doors), and that your power supply does not provide foot access to the filling station. The whole thing is fairly self-equalising though - by that I mean you can just chuck as many minecarts in as you want, and the filling station at the bottom will dispense them evenly enough that they won't crash on the way up and spill their contents.
