I wanted to know how different haste effects stack in TBC. I used a 2.6 speed weapon and looked at the character pane's attack speed display while using various combinations of buffs. I used Slice and Dice (30%), Blade Flurry (20%), Rogue Assassination Armor Set Bonus (160 Haste Rating for 6 seconds, ~10.1%), and Abacus of Violent Odds (260 haste Rating for 10 seconds, ~16.5%).
Attack Speed - Buffs
2.6 - No Buffs
2.17 - Blade Flurry
2.0 - Slice and Dice
1.67 - Slice and Dice, Blade Flurry
1.43 - Slice and Dice, Blade Flurry, Abacus
1.32 - Slice and Dice, Blad Flurry, Abacus, Assassination Bonus
Conclusion: Haste gained from abilities treats each haste source as it's own separate multiplier and these stack multiplicatively. All haste rating effects are added together to get a total haste rating and are treated as a single multiplier for your total haste rating.
Further testing could be done to confirm similar behavior with other haste rating sources like passive haste rating on armor, triggered haste rating from Dragonspine Trophy, haste from quivers, Bloodlust, or Battle Squawk.
I wanted to know how different haste effects stack in TBC. I used a 2.6 speed weapon and looked at the character pane's attack speed display while using various combinations of buffs. I used Slice and Dice (30%), Blade Flurry (20%), Rogue Assassination Armor Set Bonus (160 Haste Rating for 6 seconds, ~10.1%), and Abacus of Violent Odds (260 haste Rating for 10 seconds, ~16.5%).
Attack Speed - Buffs 2.6 - No Buffs 2.17 - Blade Flurry 2.0 - Slice and Dice 1.67 - Slice and Dice, Blade Flurry
2.36 - Assassination Bonus 2.05 - Assassination Bonus, Abacus
1.43 - Slice and Dice, Blade Flurry, Abacus 1.32 - Slice and Dice, Blad Flurry, Abacus, Assassination Bonus
Conclusion: Haste gained from abilities treats each haste source as it's own separate multiplier and these stack multiplicatively. All haste rating effects are added together to get a total haste rating and are treated as a single multiplier for your total haste rating.
Further testing could be done to confirm similar behavior with other haste rating sources like passive haste rating on armor, triggered haste rating from Dragonspine Trophy, haste from quivers, Bloodlust, or Battle Squawk.