Hi. Sorry if this is a daft question but what are the reasons for using small resonators? Lets say a chip supports both 5mhz and 10mhz. Why would you choose a 5mhz over a 10mhz? I can see that there is a slight cost difference but is there more to it? Would the chip only last half as long with a 10mhz because its working twice as hard? Does it use twice as much power?

Just another little question. If the datasheet says "DC - 20MHz clock input". That means 20MHz is the highest resonator that can be used on the chip right? Its not the rating of the internal one is it?