I really do like the seats on the DL A330 and have flown them at least a dozen times Transatlantic. I actually find them more comfortable than most of the flat beds since I never take those completely flat.
The pre-clearance and the transfer at ATL instead of the “dreaded” LHR would certainly be the game-changers for me.
Note that the arrival into ATL will be a domestic arrival and there will be no need for a TSA screening. You simply jump on the train to your next Terminal. As much as I do not really like ATL, I will take that one any time over LHR for any purpose at any time of day on any day of the year.