Rogue and Velium Swiftblade

[Lhancelot]

My question is, would my 20+ rogue be better with a 13/26 mainhand piercer and a velium swiftblade 5/24 (36% haste), or would the rogue be better with schw (22% haste) and a 10/20 or other type of offhand weapon?

From my understanding the Velium Swiftblade would quicken the rogues BS cooldown meaning with better worn haste I'd be able to BS more often. Would this do more overall damage or less than say a 10/20 offhand weapon with 22% haste from schw, seeing the Velium Swiftblade only sports a 5/24 ratio?