It would be nice if you add startup setting for load/unload speed.

Load/unload speed is already as fast as can be supported by the Factorio engine. Research inserter stack size to increase it further. You can add a mod for infinite research to increase it further than is possible in vanilla.

So it depends on inserters speed? Okay, thanks for the info.

Can you tell it is about normal inserters or stack inserters? What stack size (normal or stack inserters) i need to increase? Thanks

When you increase inserter stack size, it increases it for stack inserters at all 7 levels, and also at levels 2 and 7 it gives a bonus to regular inserters as well. There's only one inserter stack size research to work on, so that's that.

@unne BRL uses the stack size research for stack inserters. I recommend using something like https://mods.factorio.com/mod/InfiniteTech to get infinite research for stack inserter capacity.