One card being slower than others...

[Kergekoin]

Im pulling my hair here, since i cant find a solution to my problem
Im running 4 x 280x cards. All identical. All running identical custom bios.
1 card is slower than others. Does not matter if PC runs a singe, dual, three or four cards.
This slower card does not throttle or have any issues whatsoever. No rejected shares, temps are fine. Everything works just beautifully besides it being 40-50khs slower than other cards.
I tried:
- changing slots
- changing extenders
- changing bios
- changing AMD drivers
- changing config file settings
- changing power cables

Nothing works.
I use no monitor, No RDP.
Im out of ideas. Please generate some for me.
Im running W8 64bit. Using CGminer with CGremote and VNC remote.
Thank you.

[Colin Miner]

Could it be you have identified a faulty card, one that has maybe a defect in the processor?

this would explain what you have found, seeing as you have tried everything else.

[pontiacg5]

Not all cards/chips are exactly the same, play with the clock speeds and they'll probably be closer.

I have many 280x cards with clocks from 1020 to 1050, but yet they all run about 715kh/s.

[Kergekoin]

I find it extremely unlikely that one card is different from the rest of 3, which are hashing exactly the same, but thanks for suggestion.
Like i said before. This card runs perfectly fine. Just khs is lower.

[pontiacg5]

I find it extremely unlikely that you could possibly know that from your sample size of four cards. Besides, you can't get them working the same so they obviously aren't the same.

You do know how GPU chips are made right? They aim to make the best 290x chip, and any that don't make the cut are regulated to 290's, ones not good enough for 290's go to 280x cards,  then 270x, 270 and so on. This is why you can sometimes unlock a card to the higher end model, like old 5850 to 5870 flash, or even the 290 to 290x flash. There aren't enough low end chips because the process to make them is too good, so low end cards actually get better chips. Sometimes the chips are barely good enough to "be" a 280x, I'd bet a nickel that's the card you have.

Don't trust me and my rather recent experience with lots of different cards, especially 280x's, if you want though. Doesn't hurt me any.