tbh, I think you're better off dropping the green and going in a straight rakdos direction. You should think about the total damage potential of the creatures you play, not simply whether they have haste or not. Your entire deck will do more damage if your mana base is smoother (less colour screw, less guildgates) and a card like ash zealot (which is playable with a heavier red mana base) will most likely do as much damage as dreg mangler, if not more, in the time frame that this deck wants to operate in. Ditto rakdos cackler.
I sketch out a rakdos aggro list in my latest article. not suggesting it's the only way to go, but its working pretty well for me.
4x Legion Loyalist
4x Spike Jester
4x Rakdos Shred-Freak
3x Rakdos Cackler
4x Dreg Mangler
3x Exava, Rakdos Blood Witch
4x Savageborn Hydra
4x Ghor-clan Rampager
3x Dreadbore
2x Abrupt Decay
4x Overgrown Tomb
4x Stomping Ground
4x blood Crypt
4x Rakdos Guildgate
5x Mountain
1x Swamp
Obvious idea is to spam haste with the only exception being cackler and hydra, though Exava remedies them.
Perfect curve = loyalist -> Jester Spikes:cool2: -> Dreg Mangler -> Exava -> Hydra
I haven't thought too much about sideboard yet though I'll definitely include two more abrupt decays to try and stop anyone playing Blind Obedience.
I sketch out a rakdos aggro list in my latest article. not suggesting it's the only way to go, but its working pretty well for me.