Hi Bill
On Arduino IDE 1.0.5-r2 both options work.
Arduino Pro or Pro Mini (5V,16Mhz)/w AtMega328
Arduino Pro or Pro Mini (5V,8Mhz)/w AtMega328
I had resorted to 8Mhz by mistake whilst debugging other issues with USB to TTL RS232.
Since it worked for me with 8Mhz I had stayed that way. Now my RS232 issues are resolved and so seem the 16Mhz.
Great suggestions Thanks !
Simon