Gear haste cap is 25.2% so yeah you would need 26 to really cap that, but in terms of recasts Fast Cast isn't haste and doesn't count toward that 25.2 so if you had max haste in gear (not possible on rdm) you would get the Fast Cast reduction on top of that. For RDM to get close to 25% gear haste you have to chuck your Fast Cast from AF/AF2 which is a waste for recast anyway. (Max haste for RDM is walhara hat: 5%, goliard body: 4%, hq dusk gloves: 4%, speed belt: 6% and hq dusk boots: 3% for 22% haste). So basically, any dusk you can get your hands on (or feet on) will help. Would you get hq dusk just for rdm stunning? Probably not.
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