See if a different Bios is detected for any of the cards when you change the Bios switch to the side you didn't change. If they are all the same, put the Bios switch on the side closest to the I/O ports and try flashing the original Bios from the cards with only the 1750 MHz straps copied higher. After you flash the Bios try running them with a 1150 MHz core clock and 2000 MHz memory clock.