Can't say that I have.
In brief, air flows in under the HD at front-left, and out via the PS at top-right.
My subjective impressions were that installing a CD drive helped to direct airflow over the CPU, and that the train wreck pileup of RAM, SCSI and power cables right next to the PS inlet was a potential bottleneck. I'm not sure where or how it could be improved - removing the internal SCSI cables and booting externally might help, but then you lose the low profile feetsmac sex factor. Rounding the SCSI cables might lead to clearance problems over the RAM - ditto with tidying up the PS cables. But as always YYMV and I encourage experimentation.
"Come over here, Beaker, and hold these two wires. No, this won't hurt a bit"
I've wondered about placing a second case fan - either blowing in/out the Nubus port or out a new hole above the HDI video connector - but I have doubts about how that would affect airflow. I note that small fans can be found that fit nicely into the top of the 601 heatsink
, and that Output Enablers sell them with their overclocking kits. That at least should help keep the 601 cool, and it might get some more air blowing around the G3.Other options, in reverse order of ludicrousness, would be a better heatsink on the 601, a better (quieter?) PS fan, ducting, cooler-running or solid state hard drive, externalising the PS, heatpipe, liquid cooling, und so weite.
When I get back to 6100 experiments, I'll also see what could be done about supplemental cooling for the PDS G3 - maybe a salvaged sideblower fan from a notebook could be squeezed in their somewhere.
Searching the old forum archive here and the old applefritter forums should yield some more data.