About Elites -
Elites launched in April 2007. They have, at a minimum (even the oldest Elites), the 2nd heatsink.
However, some did not have Falcons, but they do have HDMI Outputs, as that was a special thing that Elites had when they launched.
The newest version Xbox 360s - all models - have HDMI, Falcons and such. The primary difference now is just the HDDs, and color.
As for making sure you get the newest one - it's very simple - just look at the unit your preparing to buy, and see if it has a 175 watt battery "brick".
If it has that 175w, your guarenteed the newest model Falcon X360 with the BenQ DVD (best kind), 2nd Heatsink and 65nm components.
The likelyhood of picking up a random Xbox 360 and it being the various models, atleast IMO would be:
Arcade Model - 100% (Arcades were made after revision)
Premium - 70%+ (totally dependant on how quick your store moves it's stock)
Elite - 80%+ (smaller manfacturing pool and brisker sales should mean more likely)
Halo 3 Edition - 95%+ (as far as I know, all were post-Falcon, but I could be wrong).
Your best bet is a true Arcade model at the moment, but I'd tend to think that by now, the vast majority of any given model is pretty high.
Back from the dead, I'm afraid.
