In a recent manuscript, we used a first principles calculation A and used it to explain experimental results B. A and B are based on existing methods, the novelty primarily lies in combining them and going from theory to real world application.
The reviewer gave several comments (fair & helpful), one of them being to divide the work into A and B. The decision was Reject & Resubmit. We (the authors) are divided on:
Submitting A as a letter (short communication) and B as a full paper to the same journal, together, explaining the changes to the editor and attaching response to reviewer.
Submitting A as a letter to a new journal and B as a full paper to the original journal, giving response to reviewer only to the original journal.
Submitting an edited but undivided paper to a lower impact journal.
Which of these is the optimal option?
The original journal has perhaps 10% acceptance ratio, the lower impact journal closer to 40% (anecdotal numbers only).
Besides the division, reviewer comments are significant and there is some chance that we may not be able to satisfy all the suggestions.
In this field, A and B are generally treated as separate domains, though this is changing now.*
EDIT: Clarification about letter and full paper: For the journals in question, a full paper reports new, original results, typically without stringent page limits (but conventionally 5000-8000 words). A letter on the other hand reports brief results of immediate interest. These often describe a breakthrough that may not be fully developed, but which opens up avenues for further work. These letters are strictly limited to 2000 words and have a cap on figures etc (typically 3 max.).