Valhalla breastplate: -55/1024 (5.37% Slow)
Valhalla helm: -55/1024 (5.37% Slow)
Total: -110/1024 (10.74% Slow)
(Note: Slow on equipment works as negative haste. Slow from spells/TPs appear to be calculated as seperate terms, but there is still testing to be done.)
Other pieces of slow, such as hecatomb work the same way. Since recast timers are floor'd SE overcompensates on slow items by giving them slightly higher slow values than listed. (Which contrasts the slightly lower values on haste items)
Casting Reprisal in either piece makes the recast go from 3:00->3:09. Using both pieces makes the recast go to 3:19. This shows that haste is still truncating the fractional part, and that V gear works the same as other slow pieces.
I first located a boundry value for reprisal @ 62/1024 and 63/1024:
(1-62/1024) * 180 = 169.102
(1-63/1024) * 180 = 168.926
Then I used Victory March at incrementing skills til I reached the boundry value:
Total Skill @ 530 = 117/1024
March + Valhalla Body = 2:49 (169 seconds)
Total Skill @ 535 = 118/1024
March + Valhalla Body = 2:48 (168 seconds)
This shows Valhalla Body is -55/1024.