A lot of people are using cases with more spacing (or no case at all), so they can leave empty slots between the double-wide cards.

Have you manually ramped that hot card to 100% fan?  It's noisy, but it might help you out.  You can also clock it differently than your other two, and spend that juice/cooling on bumping the cooler ones.

I'd imagine a good balance would be where all three temps even out at a level you're comfortable with.