On 747-400's there is a common plenum for all 3 packs, however, a baffle in the plenum ducting tends to direct more of Pack 1 air to the flight deck (if the other packs fail, plenum air can go around this baffle to the other zones).
I was originally thinking that this baffle system would provide the extra "comfort". However, on the Freighter, there is some kind of flow regulating valve between the plenum and the flight deck. Looking at the wiring schematics, the valve appears to respond to the Main Deck Cargo Fire ARM switch (it seems to run the valve to the fully closed position .., but it's difficult to tell from the schematics. It may do exactly the opposite).
I'll see if the Maintenance Manual has any more information on this.
Anyway, thanks for the feedback.
Cheers.
NSEU