New study with exit vents on the bottom, left only. Only took 4 hours of CPU time.
Wow. Definitely a BAD solution!
The Tegra 3 temp maxes at about 190°F, which would probably result in failure eventually.

[Looking back at the first solution, it's actually really good!]

So what's happening with this new solution is that air gets sucked in from the top vents by the fan and still wants to exit the heatsink from both sides.
Well, now that there's no vent on the right side, the hot air just spins and spins in a vortex and eventually causes the inlet air to be heated instantly. At that point, we're no longer sucking in cool air, and the whole cooling system is a massive failure! Glad I'm doing these simulations to ensure the vent design is adequate.




I could put ductwork in here, but that would add a lot more material, cost more, and not leave room for extra stuff one might want to add in, like USB hub & card reader.
An external outlet fan would improve cooling significantly, but it would increase noise and power requirements. This case could always be modded for an additional fan if desired.

I think the original solution with the dual-venting is the best course of action. It's already better than stock OUYA according to the simulation, so I think we're good...now that I see how bad it can get.