right next to the PCIE is true
<1mm between NF4 heatsink and the clip mechanism on the PCIE slot
<3 mm to the inside edge of my 6600GT
definitely would have to be a very slim cooler
If you had, say, a 6800u or 7800 and a Zalman, I don't think you could really do anything there except get an identically-sized (quieter) active fan
this fan does a really good job, just a little loud