Hey Therax - I've looked through the mod folders, and files and can't seem to figure out myself how to increase and decrease speeds of the loader and unloader. I see a global inserter count, extension_speed and rotation_speed variables but they don't seem to increase speed thresholds.

Currently playing a Pyanodon playthrough, stack sizes are immense and loading/unloading takes far too long. You have a "hopper" above the wagon, it should be a super fast load, and likewise unloading your dropping into a void, same theory.

Think you could steer me in the right direction?

You can add a mod that increases stack inserter capacity (see the FAQ), which will affect all stack inserters on your map, or modify num_inserters, which affects only BRLs. If you choose the latter route you’ll need to mine and rebuild any BRLs on the map for your change to take effect.

rotation_speed and extension_speed are already so high that the inserters reach the wagon and return in a single tick. Increasing them further has no effect.