I have worked at a high energy attraction at Disneyland for 4 years and Kevin is more or less correct that the FP line makes stand by longer. We are directed to not even stop fastpass at our merge point. Only the standby line is ever stopped, to let FP thru, it is never the other way around. FP always takes priority at our attraction. however we do not always run fastpass at our attraction. On a day with 37K in park we will run the fastpass line and our wait will be around 25 min. On a day with 33K in the park we will not run fastpass and our wait will range from 10-15 mintues. Obvisouly fastpass makes the wait longer for stand by.