Inga.
Från PRD själv :
Speed: When making a full-attack action, the wielder of a speed weapon may make one extra attack with it. The attack uses the wielder's full base attack bonus, plus any modifiers appropriate to the situation. (This benefit is not cumulative with similar effects, such as a haste spell.)
"Liknande effekter" inkluderar andra hastighetsvapen. (Också välsignelser av glädje, dans av tusen stycken, snabba stövlar, etc.).