Different Firestrike Score on Identical set up

[Garage PC dealer]

So I've just brought a used 1080 TI and I just wanted to see how far I could push it.

Naturally, I began overclocking using MSI afterburner, but I noticed something strange about the score I'm getting on firestrike being a lot higher compared to my current one.
For science purposes, I built an identical system to my current set up and did a controlled test.

I set both 1080TI to the same clock speed, however one of them just kept on getting higher scores for some reason, even when I lowered its GPU memory speed comparing to the other one.

Can someone please explain on why this is happening?

My test bench score https://www.3dmark.com/3dm/39723576
My current score https://www.3dmark.com/3dm/39723258?


Testbench spec
i7 8700
16GB 2666mhz * 2
H310M mobo
Samsung 850 PRO 

750W 80+ Bronze PSU
MSI 1080 TI aero

My current spec

i7 8700
8GB 2666mhz * 2
Z370 mobo
Samsung 970 EVO 

750W 80+ GOLD PSU

inno3d herculez 1080 ti