Super:
My timing page has the following paragraph:
Quote:
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If one Pokemon is holding Quick Claw and it activates for this round (20% chance), or it is holding Custap Berry with the appropriate amount of HP remaining, it strikes before the other Pokemon. If this condition holds for both Pokemon, the one with the higher Speed strikes first; ties in Speed are broken at random.
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So in that case, if both items "activate", then the effects cancel out and the Pokemon's Speeds are used instead.