hello!iv read on other threads that impale procs area damage on all 3 daggers no less but im not seeing or hearing any area damage proc,
I don’t think you can see it or hear it, but it’s happening 
impale has a chance to proc AD on ANY dagger. So, if running lightning impale s6, that’s 9 daggers…if the cold variant of the build, then in theory, as many monsters as are in a straight line and can be hit by your daggers.
The cold build in theory has a chance to do more damage than the lightning build, at least, if monster density is very good in the GR.
Remember, AD procs (chance to proc) on hit, and then if successful, affects any monsters within a 10 yard radius of the monster that procced AD.
I am not entirely sure if you can have multiple procs of AD running within the 10 yard radius (for example, dagger hits monster A, procs AD, affecting all monsters within a 10 yard radius, and then One of the other monsters within that 10 radius also procs AD, meaning some monsters may be hit by 2 lots of AD proc damage).
There are many mechanics in the game where Blizzard has not been clear whatsoever on how the mechanic works.
I personally prefer to keep the shoulders with dex/vit/AR and CDR and have IAS on the dagger - yes, it can, and does do less damage than AD (when AD triggers of course), but remember, AD only has a 20% chance of triggering. IAS on the dagger will affect EVERY dagger, EVERY time.
I tested both AD and IAS in s15, and much preferred IAS. Quin69 has an excellent video on AD on his YouTube channel (it’s an old video, but is still 100% valid with today’s game).
edit: there is no on screen sound or effect that shows AD has been triggered (bad game design imho). There’s no reason why Blizzard could not have developed a occulus style 10 yard display ring when AD is in effect. None at all. AD will not show as a Red crit either, it’ll just show like any other on screen damage (no crit) number.
From what of I noticed AD must be over 100% in grift 115+ (solo) to function good. I have a hard time to stack it since Ive been chasing a knife with AD + Speed and good min-damg but never found one despite 3k FS and maybee lik 5k death breaths in cube. But if U get AD on shoulders then you only need 20% on ring or quiver for 90% AD or else you will kill the elites and all greys have their hp at full.
AD over 100% will work no matter what the GR lvl.
I tried AD in s14, and IAS, and went with IAS in the end. IAS always works, rather than the 20% chance to proc AD…d3planner showed IAS was slightly better too, at least on simulation.
You’re gonna hate me, but I got a perfect primal karleis point from DB upgrading after my 12th go this season…IAS and LPK as a secondary…can’t ask for better!
If you use BotP then IAS is very strong probably the best stat. But with pain enhancer (the most common for hard pushing) AD is just as good or better since you already have a shitload of IAS from the gem.