From the game's unrealscript code in ShockPawn.ini and ModEffects.ini
Base Player speed GroundSpeed=450.000000
[ShockPlayerPlasmidEquipped_FastTwitch_spec]
ClassName=Class'ModEffectSpecification'
Precache=True
ModDefinitions=(GroupName=GroundSpeed_Bonus,Operation=OP_Addition,UseExternalDuration=False,Duration=0,UseExternalValue=False,Value=10,Description="Increased speed from the fast twitch plasmid",UsePlasmidSlotBonus=False,PlasmidName=FastTwitch,BonusWhenEquipped=0,BonusPerSlot=0,BonusDurationPerSlot=0,AddUnique=False)
ModDefinitions=(GroupName=WrenchFireRate_Bonus,Operation=OP_Addition,UseExternalDuration=False,Duration=0,UseExternalValue=False,Value=0.25,Description="The player fires the wrench faster",UsePlasmidSlotBonus=False,PlasmidName=FastTwitch,BonusWhenEquipped=0,BonusPerSlot=0,BonusDurationPerSlot=0,AddUnique=False)
[ShockPlayerPlasmidEquipped_FastTwitchTwo_spec]
ClassName=Class'ModEffectSpecification'
Precache=True
ModDefinitions=(GroupName=GroundSpeed_Bonus,Operation=OP_Addition,UseExternalDuration=False,Duration=0,UseExternalValue=False,Value=20,Description="Increased speed from the fast twitch plasmid",UsePlasmidSlotBonus=False,PlasmidName=FastTwitch,BonusWhenEquipped=0,BonusPerSlot=0,BonusDurationPerSlot=0,AddUnique=False)
ModDefinitions=(GroupName=WrenchFireRate_Bonus,Operation=OP_Addition,UseExternalDuration=False,Duration=0,UseExternalValue=False,Value=0.5,Description="The player fires the wrench faster",UsePlasmidSlotBonus=False,PlasmidName=None,BonusWhenEquipped=0,BonusPerSlot=0,BonusDurationPerSlot=0,AddUnique=False)
This is why this tonic line does not seem to increase your movement speed, adding 10/20 to the player's base speed of 450 means a negligible 2.22%/4.44% increase.
