I don't have one, so I wouldn't be able to test it~ But if you wanted to run the basic test you could do the following:
1) DRK /w Dread Spikes
or
PLD /w Reprisal
2) BRD /w various skill gears and Victory March.
Have the DRK or PLD only equip the haste helm~
Have the BRD sing Victory March /w +2 Instrument and +0 skill gear~
Have the DRK/PLD cast Dread Spikes/Reprisal~
Record the total sing/wind skill and recast from Dread Spikes/Reprisal~
(Note: Make sure to use the recast found in the menu when highlighting the spell~)
Increment Victory March by 1/1024 by equipping sing/wind skill~ (Use: http://www.trutlels.com/omenfiles/vicmarchchart.JPG for reference if you need~)
Repeat~
When you find where the recast changes, you'll be able to deduce the exact value of haste from the helm~
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