So my setup is two reference xfx 7970s stock cooling. The primary card is the higher card on the motherboard. At idle with default CCC fan settings, the primamy card holds around 63-66C while the secondary is 41ish C. I'm waiting on my waterblocks to come in later this week but in the meantime this is where i stand with a few questions. Is an idle temp of 63-66 bad for the cards? Secondly, using afterburner I adjusted the fan controls and it seems the card will hold 50C at 49% fan vs 63-66 @ 30% fan. Is the wear on the fan worth the gains in idle temps? Or am i worrying about something that i dont need to be? Ambient room temp is probably around 75-80F though it does seem to get hot in the room when i start gaming. I also dont like the card getting warmer then 80C does that justify cranking the fan speed up to 100% to keep it below?
In a crossfire setup, the top card will always be hotter. It wouldn't hurt your fans to run them at 50% instead of 30% and once your waterblocks come, you won't have the issue at all.
Even with an empty slot between there is much less airflow to the top card which results in a higher temp.
If you are worried about your top card, switch them around. Put the card that is currently in the second slot on top, and vice versa. Re-boot and see what your temps look like. If in that configuration the same card is hotter (even though it is now on the bottom) you may have a problem with that card. But, if the temp profile looks about the same, it can be attributed to the airflow in your case.
Once they are water cooled, they should both be roughly the same temp