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Crossfire, Lowest Common Denominator?

Question asked by gmart84 on May 9, 2018
Latest reply on May 22, 2018 by wimpzilla

It had been years since I built a gaming machine and over the past three months I have cobbled a new one together as i forgot how much i enjoyed the building process.  My build is as follows:

 

i7 8700K

Asus ROG STRIX Z370-E

16 GB Corsair Vengence RGB DDR4

2 x Corsair Force LS SSD

2 x Corsair Force GT SSD

2 x Lite On SSD

Corsaive HX850i

Thermaltake Core P5

EKWB Custom Loop Cooling

XFX RX 580 8GB (Primary) (Purchased when RMA took three months)

XFX RX 570 4GB (Linked) (From RMA'd RX 560)

 

I have a couple of questions.  One, is that I was under the impression that when running in crossfire mode all cards follow the lowest common denominator, so in my case they should both act like the RX 570 correct?  That did not seem to be the case at all.  I did some testing in Far Cry 5 and while it absolutely shows that it was running in Crossfire, it was doing so at the RX 580 speed and using all 8GB of VRAM.  Did I do something wrong?

 

My second question is that when I go into Radeon settings I see that the core clock and memory speed of the RX 570 are wonky, it says 1100 core clock and 1850 memory speed when it should say 1286 core clock and 1750 memory speed.  What could cause this, is it a function of the Crossfire feature?

 

I am thrilled with the results but want to make sure I am not doing something wrong.

 

Far Cry 5 (3440x1440, Ultra, RX 580 Only)

Minimum FPS = 36

Maximum FPS = 52

Average FPS = 41

 

Far Cry 5 (3440x1440, Ultra, RX 580 + RX 570 CF)

Minimum FPS = 43 (+19%)

Maximum FPS = 79 (+52%)

Average FPS = 63 (+50%)

 

As I said the gains were awesome to see from the entire situation.

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