Based on my experience upgrading with 500-milers two years ago and more, SFO-JFK will cost six 500-milers per pax each way, not five. It is over 2,550 miles one way. (2,586 or something like that.)
But, for example, SFO-PHL will cost only five 500-milers. It's 2,521 miles one way (thus meeting the less than 2,550 cutoff mark).
Kathy