Arduino Pro Mini 3.3V Sampling Frequency

What is the maximum frequency for the Arduino Pro Mini 3.3V. I know that it has an internal clock of 8MHz but what is the maximum frequency it can send data at. I am using a 555 timer to set the frequency but what is the maximum frequency to send data from the analog pins.

Thank you!

100-150uS per ADC read itself (I don’t know what it happens to be for an 8mhz one under Arduino and don’t feel like doing the legwork)

But how are you getting the data off it? That may be a limiting factor - certainly if using serial at the normal speeds it would be!