Yeah, the head size of the TXD is more like 95 sq-in, not 89. Definitely longer than the TXP or other "Pro"-series 600cm2/89.5's.
In comparing the TXE and TXD: I think you'll find that each generates (or transmits) power differently. The TXE, as its sweetspot is further from your hand, has more "leverage" when the ball is hit cleanly. The TXD, with its "snowshoe" head, has longer mains and will tend to trampoline the ball moreso. Its sweetspot seems much closer to one's hand.
In its day, the Director-series frames were Head's closest foray into Oversize hitting area territory - they were trying to engineer a solution that had as large a head as possible, but as little string 'trampoline' (the main complaint of the Prince OS frames back in the day, and the primary reason why the pros and purists steered away from them, leaving them for the beginners, weekend warriors, and doctors' wives) as possible. In 1986, they relented, and introduced the Masters (102 in2/660 cm2) head size, which was more elliptical and far less ovoid.
If you have an opportunity to hit your two ur-TX's back-to-back, kindly let us know your impression of each, and how they compare!