Why does the serial monitor only go upto 115200 baud when the avr can go faster

You can always use a PC terminal program as your serial monitor, there are a ton of free ones available with many more features then the bare bone arduino serial monitor. I use Brey terminal, and you can keep it opened on your desktop as it has a connect/disconnect button so that you can easily free up the serial port for uploading with the IDE and then connect for monitoring.

Lefty