So I've been messing around with my G4DA again (upgraded circa 2007 with an OWC CPU, 1.467 GHz). The beast I am trying to tame is heat. I have four AGP GPU cards for this machine I can swap in and out. The stock GeForce 2MX works fine, as does a 4MX upgrade I acquired a couple years ago. These cards seem to have no heat-related instability. I also have a 4Ti 4600 and a FireGL X3 (the latter appropriately taped) and they both scream on this machine.... but I can not run them for more than a few minutes without crashing or freezing with the Mac's side door closed. When I open that door wide open, both cards are very stable and can run for hours on end doing fairly intensive stuff. That tells me that with 99.9% certainty the culprit is heat. It's not just that these other two cards generate more heat but also that their form factor prevents sufficient air flow when the door is closed. I'd love to be able to use one of these two as my regular "go to" GPU on this machine but the heat issue makes me shelve them most of the time and stick with the 4MX (at least I can use DVI output with it, as opposed to the 2MX). I'm interested to hear any (hopefully not too draconian or expensive) suggestions y'all may have with respect to heat and airflow in this machine. I'm willing to concede the X800 may never work with the door closed, but I'd like to think the 4Ti could be made to be stable.