You're overthinking the cooling thing.
As long as there's a 12V fan running (even running at 5V), anywhere near the top of the cab, blowing up and out, it's going to suck enough cool air into the bottom of the cab, to cool everything in the cab.
Even with the relatively non porous Pole Position EMI cage? Doesn't seem like much air is moving through that at the moment.
You had mentioned a while back that a cage + fan is better than running without a cage, which is better than just a cage without a fan (for Pole Position).
I did order a bunch of 12v fans to try to change over some of my other noisier games (lookin' at you Qix and Firefox).
Also, if you're having a problem with interference as the game is warming up, I'd still be less inclined to think it's a cooling issue, but rather something else not being right, and the temperature is just bringing it out more. Tens of degrees shouldn't make a difference to a healthy game. You want to focus on finding the root cause here, not treating the symptom.
What I saw when the game warmed up previously was weirdness with the monitor.
So, I'm trying to hunt down the remaining issues with the display. To that end, I rigged up a mini-me test.
This has revealed the following tidbits of information:
1) All the pulsing and jitteryness of the disco is from the disco itself. The other monitor was unaffected.
2) The interference to the monitor is coming in through the game board wiring/video feed. It isn't present when I use the TPG on the disco while the game board is running, regardless of if the monitor frame is grounded or not. Probably because there isn't a ground loop in that case. (Nor was it present on the little monitor, though I didn't try tying an earth ground to it)
3) The screen blanking issue I described earlier is definitely a gameboard problem. It happens on both monitors.
4) The video ground is critical. I can't just use the earth ground (I tried that one for funsies)
To address the pulse/bloom on the disco monitor, I'm looking at replacing the voltage regulator, the filter cap, and one other crusty cap I Identified on the disco... (When I had ordered the cap kit for the Disco, it was missing 5-6 electrolytics that are present on the PCB. )
This includes this crusty fellow.
I didn't have the appropriate cap on hand when I initially capped this and forgot about it. Not anymore. Ordered the proper cap.