Good point. I went with these:
https://www.tirerack.com/tires...tnum=245WR7RT615KPXL
https://www.tirerack.com/tires/tires.jsp?tireMake=Falken&tireModel=Azenis+RT615K%2B&partnum=94WR8RT615KPThe RT615 rear is 5 pounds lighter (!) than the RT660 and are rated better (and a little bit less expensive).