If the workout stated that Webb ran 20x400m at 58sec with increasing rest would you be blown away? If it went into detail that it was 5 sets of 4x400m w/3min rest between sets and 60-120sec increasing rest between intervals (for a dude running 3:40 for 1500m casually that season) would it rock your world?
Webb did a very impressive workout, but I wouldn't say it qualifies as "the most famous" (implying it is arguably the greatest). His entire workout averaged 58sec; his first 16 reps averaged 59sec. The first half, considering the rest, was pretty mellow for him. Combined together with the ramped-up second half, it was a great workout, but nothing truly insane.
I'm not sure if they're better, but I've always been really impressed by some of Kennedy's workouts from the late 90s are more impressive:
1) 1998: 1600-1200-800-400 step down w/3min jog between: 3:57, 2:56, 1:55, and 55
2) 1996: 12x 400m (not 20...), but consistent short rest:
4*400m (:59.6, :59.2, :58.1, :59.7)(:55) (3:00)
4*400m (:59.6, :59.4, :59.1, :58.1)(:55) (3:00)
4*400m (:59.0, :58.8, ;59.5, :58.1)(:55)
Or to compare Webb's pinnacle of fitness to Bekele in his prime:
8 each, alternating: 400 in 52-54, 200 in 24-25) w/ 90sec-2min rest in between. Lots of rest, but crazy fast. Fast at a level wayyy beyond that of the "miler" Webb.
I'm sure Rupp has dropped some crazy stuff like this that we don't know about.