Ironically even though I agree Spyglass is a challenging course, when I made a trip to the peninsula in 2007 my best round was at Spyglass (79) from the second set from the back (blue?). My next best round was the tips at Pebble Beach where I bogeyed the final three holes for an 80. Contrast that to Pasatiempo, where I struggled mightily except for a birdie at 18. My other three rounds were somewhere in the 80's as well I think.
Every course on that trip was challenging, including the three mentioned. None of them are even close to what I would consider the five hardest courses I've played. Off the top of my head, that list might start with Butler National, Conservatory at Hammock Beach, Pete Dye Course at French Lick, The Concession, and Painted Valley at Promontory (Utah).
I don't think Spyglass gets nearly enough credit from some members of this board. I think its rated pretty accurately as a borderline top 50 course in the USA.