atmega328: external crystal oscillator and uart
There are some specific crystal oscillator frequencies named 'UART friendly'. Using these frequencies would lower % error in UART communications. Please refer to the table in the datasheet, in chapter named "BAUD rate settings" (datasheet of ATMega328: '24.11. Examples of Baud Rate Setting'). There are tables to show error percentage. What to look at is "Error" column. fosc is selected oscillator/crystal frequency. For succesful UART communication you aim for less than 3.5% Error.
 Your crystal speed should depend on your desired communication speed, for example for me the preferred ones are 11059200Hz or 1843200Hz.  



or below:


With raising frequency you may expect power consumption and the chip's temperature rise, anyway I wouldn't worry too much about life shortening. More important here would be power consumption rise. 
 Do you want the chip(device) to be battery powered? To save on energy you can also consider lower frequencies like 1.8432MHz or 3.6864MHz.