Crossfire HD 6870's and spacing

[aka.Goliath]

I have an Asus P8Z77-V PRO with an Asus HD 6870, I want to get a second one in crossfire but I am worried about the spacing between the two cards. There would be a <1cm (max) gap between the back heat sink and fan. Is this enough space between the two cards to allow enough air in to cool sufficiently? I can't use the bottom PCIe slot as it is to close to the PSU and is only PCIe x16 (mode x4). Any info would be great. My last resort would be water cooling but it can get very expensive and make it cheaper to get an equivalent single GPU

If I were to look at an equivalent single GPU what would compare directly to two HD 6870's in crossfire? nVidia or AMD

 

[Archer]

1cm will be enough depending on the fan profile you setup
You can actually also use the x4 slot if you are still worried, it will hardly make a difference (less than 2%)