I have no foundation, except experience, for the following statement. I have never had any precision problems using either crystals or oscillators when following this rule: If ONLY the '51 use a crystal, if any other pin driven by the clock, use an oscillator. Some of the data sheets indicate that you can drive a CMOS load from the '51 clock, I would'nt.

Out of curiosity, why do you need a precision better than say .1%.

Have fun,

Erik