So do I choose 4MHz or 32 MHz ?
I have it on good authority that the PLL speed is the one to use. Thanks Bruce!!!

What radio modules are you using? I have only used the ones from rentron.com.

As for reliability, all of the serial methods (HSER,SER,SER2..) are good. Are you planning to use interrupts with the serial input or just wait and time out, check later sort of thing?