How much cooler can a geothermal system cool my house?

If it is 90 degrees or more outside how low a temperature can a geothermal system get down to? Will it be as cool as a traditional air conditioning unit?|||A properly sized system is not dependent upon the temperature of the "source" for it to work well. An air to air air conditioner, an air source heat pump and a ground source heat pump (geothermal) system should all work if sized properly. What is different will be the amount of equipment and energy required. A ground source heat pump will be far more efficient and use less energy than other possibilities but may cost considerably more. As a side benefit you can get heat.