How to select ARM controller

Hi,

I used to work on project where the controller is already selected by the experts. and from my experience i know to look in to following parameter on a controller is really required.

1. Interface required for our application.
   1. SPI, UART, I2C etc
   2. max speed max node supported.
2. Power requirement
3. Memory requirement
   1. do we need external Flash, EEPROM requirement etc.
4. Max system clock speed 
   1. I can determine the how fast we can execute instructions.

Anyone can suggest a theoretical approach or any methodology, how the experts do this selection.