Results:

Otsu - 101ms

Sauvola 1 - 263ms

Sauvola 5 -3407ms

Differences

Otsu / Sauvola 1

Otsu / Sauvola 5

Sauvola 1 / Sauvola 5

Code

($ (image-load "lena128gray.jpg")

   (//
    ('(timer-start)
      (otsu)
      '(timer-print "Otsu")
      (save "otsu.png"))

    ('(timer-start)
      (sauvola (box2d 1))
      '(timer-print "Sauvola 1")
      (save "sauvola1.png"))

    ('(timer-start)
      (sauvola (box2d 5))
      '(timer-print "Sauvola 5")
      (save "sauvola5.png")))

   (//
    (#(diff $1 $2) (save "diff-otsu-sauvola1.png"))
    (#(diff $1 $3) (save "diff-otsu-sauvola5.png"))
    (#(diff $2 $3) (save "diff-sauvola1-sauvola5.png")))) 


> Otsu: 101ms
> Sauvola 1: 263ms
> Sauvola 5: 3407ms