I have recently submitted a 40 pages paper to a journal, say (A). After about 6 months, the editor let me know that several reviewers have declined to review my paper, and so he decided to reject the paper. He suggested that I submit my paper to a more specialized journal. Journal (A) is already a specialized journal and I only know 1 journal more specialized than (A), let's call it journal (B). So, one of my options is to submit my paper to journal (B) and accept the risk of a similar feedback from the editors of journal (B), of course after several months.
In the mean while, I think the main reason several reviewers declined to review my paper is that (1) my paper is relatively long, (2) My paper consists of two parts and each part addresses a different subject. Therefore, the set of reviewers who have expertise in both subjects and are willing to read and review my paper is very small. Due to these facts, it is very likely the editors of journal (B) face the same problem. So, as the second option, I am thinking of splitting my paper into two shorter papers each consisting only one subject of my original paper. Regarding this option, I can think of the following pros and cons:
(i) There are a good number of experts in each subject and it is fairly easy to find a reviewer for each one of my shorter papers.
(ii) This facilitates the referee process of each paper and hopefully reduces its time period .
(iii) Two papers (each approximately 20 pages) look better than one paper (approximately 40 pages) in my CV.
(a) The second part of my paper depends on the notations and results of the first part. So the reviewer of the second part may prefer to read and review the whole paper at once, or even worse he/she may call the paper containing the second part incomplete.
(b) Part of the motivation of the developments in the first part of my paper comes from my work in the second part. By separating these two parts, the reviewer of the first part can complain about the lack of enough motivations and justifications for my results. In my opinion, it is not a serious problem because I will explain the application of my works which is going to appear in the second paper. But I am not the person who makes the final decision and the reviewer may blame this and reject the paper.
(c) I can imagine that it would be a difficult path to follow the referee processes of two related papers simultaneously, because of the following reasons: It is possible that the opinions of reviewers of the shorter papers differ significantly. Or it is possible that these papers get refereed in two very different time periods. It is also possible that one of the papers gets accepted and the other one doesn't, which is a pretty ugly situation.
Unfortunately, I have faced each of the above difficulties ((a), (b) and (c)) in my previous submissions and I know how they can ruin my papers. In fact, the main reason that I organized my results collectively in one paper was to avoid the above issues. But now that my paper has been rejected without any peer review, I am considering the option of splitting my results into two papers. So, I have the following questions to ask from people who have more experience and have been involved with similar situations (for instance as an editor or a referee):
(1) What do you think about the above pros and cons? Do you know any other pros and/or cons? And, is it a good idea to split my paper into two shorter papers?
(2) If it is advisable to split my paper into two papers, should I submit them to the same journal, (maybe same editor), or should I submit them to different journals according to the best editors who can handle my papers?