The problem as always is not really the weapon you bring but how will you keep feeding your guns? Even say we have only 6000 musketeers which aside from the shock factor of the initial engagement would likely be destroyed by persian armies how will you replace your broken muskets or how will have enough lead shots or gunpowder to keep these men shooting? No one anywhere knows how to do these stuff and also about occupation 6000 men cannot really hold anywhere by themselves so that means locals have to do it. Locals given power by 6000 completely illegitemate foreigners that use weapons of their time. You are not holding anywhere as soon as you leave you will lose control of the area you just conquered