[Groucho2004]

Quick test on my i5-2500K (Sandy Bridge):

Script:

blankclip(length = 1000, width = 5000, height = 3000, color=$005B8B).killaudio().assumefps(50, 1)
#flipvertical()
#fvertical()

Result with "flipvertical()"

[Runtime info]
Frames processed:               1000 (0 - 999)
FPS (min | max | average):      124.8 | 148.5 | 141.8
Memory usage (phys | virt):     121 | 120 MB
Thread count:                   1
CPU usage (average):            24%
Time (elapsed):                 00:00:07.050

Result with "fvertical()"

[Runtime info]
Frames processed:               1000 (0 - 999)
FPS (min | max | average):      121.3 | 141.3 | 135.9
Memory usage (phys | virt):     121 | 120 MB
Thread count:                   1
CPU usage (average):            23%
Time (elapsed):                 00:00:07.360

This is on XP, so no AVX optimizations used.