The video you pasted shows true potencial of GTX 1070, but for that you must have powerful CPU and powerful RAM (as he has) - for gaming at higher frame-rates!
Noone on this forum as it seems would agree on that (that also quite good CPUs like i7 4771 and not so slow ram DDR3 1600MHz could be a reason for bottlencking in certain games).
I'm experiencing similar/or same issues as you (with i7 4771 CPU and DDR3 1600MHz RAM), large FPS drops when GPU usage drops and few CPU cores are hitting about 80-92%, which can easily be NOT showing 100% correctly.
For example: at one instance I got 98% GPU usage and 150FPS+ then when I turn camera around towards people and chaos GPU usage drops to 60% or less and FPS drops to 80s or something (in Battlefield 4).
Because I don't want to feel nervous and angry anymore (because this really stressed me out when I replaced GPU with GTX 1070) I (for now) decided and "fixed" my issue with this: - only if you have 60Hz monitor or perhaps 75Hz where you can maintain solid 60 or 75 FPS:
Battlefield 4 in-game settings:
RESOLUTION SCALE: 150% (it'll provide awesome f* quality at least on my 2560x1080@60Hz display), 130% looks nicely too.
Settings: Everything ULTRA, only Effects at HIGH + 4x MSAA (if you don't like MSAA or you'll see FPS drops (which on 60Hz/60FPS you shouldn't) you can turn that off)
FOV: I have 70 (+86) on 2560x1080 - set it yourself as you feel comfortable
V-SYNC: ON - don't be scared of in-put lag because with setting below you will "almost" remove it completely.
In-put lag removal: In Riva Tuner Stasticts Server which I'm using with MSI Afterburner I cap my FPS to 1 frame less then refresh rate of monitor - so to 59 with 60Hz monitor to almost completely REMOVE in-put lag.
If you have 75Hz monitor cap them to 74.
RESULT:
Butter smooth gameplay without stuttering and without screen-tearing, constant GPU usage around 70%-90%, beautiful and much sharper, crispier and better graphics (because of 150% resolution scale and all Ultra settings), constant 59FPS with ZERO drops, even cooler CPU and GPU temperatures because of capped FPS which makes breathing time for both CPU and GPU.
I've set this settings for every game I currently play (Battlefield 1, Battlefield 4, Just Cause 3, Far Cry 4) and will play in future - it's much better experience and gameplay without getting annoyed with GPU not being fully utilizied and FPS drops.
I really suggest this to you.
I suggested same thing to 2 of my friends and they are thrilled with gameplay smoothness and barely noticable in-put lag.
Try it out - play like this for few hours and tell me how you feel.
Have a nice day.
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