I know 11.0592 is the best for serial comm but sometimes if apps demands you need to use 12mHz crystal and still communicate
A 9% speed improvement?? if your app is that close to the edge, you should use a faster processor.

You need a slower crystal then use 3.6864Mhz perfecto for comm slower m/c
Why on earth would you do that?

each cycle will give me exactly 1 uS timing instead of 1.085uS as in 11.0592Mhz
If that is a problem, you need a better calculator.

If the above comes out 'harsh' please understand I have heard more BS about using 12 MHz crystals "without problems" than many other things.

Erik