Your current weapon is used. To compare a two-handed weapon with a one-handed weapon + off-hand, run multiple simulations.
Enchantments are copied from your currently equipped items.
Sockets and neck/ring gems are copied from your currently equipped neck or your first ring.
Rings and trinkets are tested in both slots (unless restricted by the “Unique-Equipped” limitation).
Dual-wielding classes test weapons in both hands.
Simulation time increases as the number of potential upgrades grows.
Droptimizer always uses Smart Sim.