All haste is delay reduction, there are limits to cumulative haste from multiple sources (and level-based cap on total aggregate haste).
for melee & combat skills you may have:
1 haste buff (if multiple best is used)
1 haste item that is not a quiver (if multiple best is used)
for archery:
1 haste buff (if multiple best is used)
1 haste item that is not a quiver (if multiple best is used)
1 quiver (if multiple best is used)
the wiki has a decent explanation in greater detail
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