Xenons and Zephyrs (2005-2007) are the consoles that are better of as doorstops.
Falcons and upwards (2008-201x) are decent machines.
I got a Falcon RGH meself, used it for thousands of hours, still going strong.
totally!
on my side, i been lucky with my Zephyr, wich i still have fully fonctional with cpu temps going maximum to 70*C (the rest stays under 50*C) , i added some 'coil' parts on the GPU's coil, some heat-foam on the RAMchips and added a tiny fan plugged in the same connectors as he normal fan so this way it follows the same fan-speed as the basic fan.
I had this Zephyr for sooo long, pretty happy its still in great health lol
i bought it for 20$ a long time ago in a video game shop, the guy said it was rrod and he didnt know what to do with it, and since i repaired lots of rrods i bought it in a heartbeat..and when i arrived and unnassembled it, the only issue causing the rrod on this one was a big layer of dust in the fan and the fan wouldnt turn at all..once removed and cleaned it ran perfectly, it wasnt even really rrod
i still reflowed it to make sure it doesnt rrods.. ...without any fan mod, i think it heats-up more thyen any pc i seen
on another topic, does anyone know the proper pinout for the dual fans in he 360 fat?
you can use the voltage of the disc drive to power your fan to 12v, by splitting the wires behind it and connecting the ones from the fan.
As for adding your new fan, i suggest plugging it to the same wires as the default fan in the console by splitting the default fan's wires. But if you plan on adding it elsewhere in the console, you can use most of the 6v sources on the board, like the ones from USB ports.
Have fun and take your time.