A dozen - that's pretty serious. Can you explain the bit about "fast signals nearby" a little more. What exactly are you talking about here? I'm not even sure what fast signals on an Arduino evenmeans, as I/O is pretty slow in general. The crystal oscillator is by far the fastest. Thanks.
Pic of my board: http://www.bajdi.com/wp-content/uploads/2012/12/bajduino-mega-3A.jpg