Answer

First you need to check the cable types. According to the information of INTEL Developer Forum, passive lower cost cables can only get half speed of active cables. And the actual speed would vary from cable quality, storage write/read speed, operation system, drivers and firmware versions.
https://thunderbolttechnology.net/sites/default/files/IDFSF15_HSTS004_100a_1.pdf

Models

  • GT72S 6QE Dominator Pro Heroes Special Edition(4K)
  • WT72 6QK
  • GS60 6QC Ghost
  • GT72S 6QD Dominator Heroes Special Edition(4K)
  • GT72S 6QF Dominator Pro G 29th Anniversary Edition
  • WT72 6QJ
  • WT72 6QL
  • GS60 6QE Ghost Pro(4K)
  • WS60 6QH
  • WS60 6QJ
  • GT72S 6QF Dragon Edition G 29th Anniversary Edition
  • GT80S 6QD Titan Sli Heroes Special Edition
  • GT80S 6QF Titan SLI 29th Anniversary Edition
  • PX60 6QD
  • WT72 6QI
  • GT72 6QD Dominator G Tobii
  • GT72S 6QE Dominator Pro G
  • GT72 6QD Dominator G Heroes Special Edition
  • GT80S 6QD Titan SLI
  • GT72 6QD Dominator G
  • GT72S 6QE Dominator Pro G Heroes Special Edition
  • WT72 6QM
  • GT72S 6QD Dominator G
  • GT80S 6QF Titan SLI Heroes Special Edition
  • GT72 6QE Dominator Pro G Heroes Special Edition
  • GT72 6QE Dominator Pro G Tobii
  • GT72S 6QF Dominator Pro Heroes Special Edition(4K)
  • PX60 6QE
  • GS40 6QE Phantom
  • GT80S 6QE Titan Sli Heroes Special Edition
  • WS60 6QI
  • GS60 6QD Ghost
  • GT72S 6QE Dominator Pro G Tobii
  • GT72 6QD Dominator Heroes Special Edition(4K)
  • GT72 6QE Dominator Pro G
  • GT72S 6QF Dominator Pro G Heroes Special Edition
  • WT72 6QN
  • GT72 6QE Dominator Pro Heroes Special Edition(4K)
  • GT72S 6QD Dominator G Heroes Special Edition
  • GT80S 6QE Titan SLI
  • GT72S 6QD Dominator G Tobii