The base game tops out at Tier 3 belts. For a megabase, these are essentially clogged arteries. The Modular Conveyor mod introduces Tier 4 (x3 speed) and Tier 5 (x5 speed) belts. When combined with faster sorters, your main bus stops being a traffic jam and starts being an autobahn.
Some popular mods for Automation Empire include: automation empire mods better
: The gold standard for rebalancing the entire game. The base game tops out at Tier 3 belts