With dul wield optimal with 14+ cdr is max 15 aps (both cospris triggering spells efficient), with one handed optimal is 7.5. 15 aps is a bit hard to get so just get 7.5 or 7.49 and you are fine. Never go 7.51 or more. Remember that every increased aps matters example, onslaught, elusive, frenzy charges etc.
I am no sure If I understood it right but here is long writing about it:
https://www.pathofexile.com/forum/view-thread/2676194