Someone had mentioned earlier in this thread that voltage was linked to clock frequency, so thats what I was going off.
Comms is not an issue as I'm programming the 328 in an Arduino then taking it out and dropping it in my PCB.
Marvin Martian, why do you think you would need to reprogram the bootloader?
As I understand it, clock speed is hard-coded into the bootloader, so changing the crystal isn't enough to change the speed. You would need to program a new bootloader in as well.
Why reprogram the arduino when you can just buy a crystal for 2 bucks
The last thing that needs to be done is adjusting the Arduino IDE preferences file: ~/Library/Arduino/preferences.txt on the Mac and C:\Documents and Settings\<USERNAME>\Application Data\Arduino\preferences.txt on Windows:The build.f_cpu preference needs to be set to 1000000L