Adding more motors will generally give you more power, meaning you can lift more. You will however need a bigger battery to get the same hover time, since more motors will use more power as well. So there is a trade off between being able to lift a lot, and flying for a longer time.
Another advantage of more motors is that you can maintain maneuverability even if you lose a motor. So if you are carrying some expensive equipment or doing something critical, six or even eight motors might be preferable.
I'm not aware of any simulators that can test this accurately, but you can use this online calculator to test different configurations. I assume that is close to what you want? Most of the options require a payment, but you can probably get an idea of what you want without that.