gpu usage problem

Hello everyone! Recently I had the opportunity to put together a 6x 1070gtx mixed brands.
When I use hashcat piping one of the c++ scripts found on here ( https://hashcat.net/forum/thread-6170.html ) the GPU usage is not 100% all the time. I'll explain better with pics.

HW:
  -6x 1070gtx
  -CPU i7-4790
  -MOBO H81 Pro BTC R2.0
  -RAM 2x 8GB 1333 MHz

SW:
  -Ubuntu server 16
  -nVidia driver 384.90
  -hashcat 4.2.1

If I run:
./ua | hashcat64.bin -m2500 -w4 lollo.hccapx
I've notice that the GPUs go from 100% to 0% and vice versa all the time as the pics shows. I guess that is the CPU not able to create fast enough the wordlist?
Any idea on how I can improve the performance of my rig?

Also if I run:
hashcat64.bin --stdout wordlist.txt | hashcat64.bin -m2500 -w4 lollo.hccapx
I get something way worse. But if I run it in straight mode it will keep a nice 100% on all the GPUs at all the time.


If you need more info just ask me, I will reply as soon as possible!!
Thanks in advance!

  hc2.jpeg (Size: 459.36 KB / Downloads: 0)

  hc1.jpeg (Size: 479.86 KB / Downloads: 0)