I usually consider the number of issues per year. But I want to know other strategies you usually do to estimate the editorial speed? Any idea where can I consult this?
I personally feel how fast the editor responds and manages the review process and takes subsequent decisions is a deciding factor. If the editor is quick, this decisions should come in less than a month as Dr, Kamal said. Number of issues per year might be a different factor because the issues are decided mostly depending on the submissions to a particular journal. When submissions are less, issues are less. If they increase suddenly, then I have seen editors using a supplement issue in between the scheduled issues as a measure to manage excess submissions.
As you are talking about editorial process speed, it mainly concerns with the paper handling process. Hence the faster a decision is reached regarding your submission, the higher the speed will be.
As Chief Editor, I think that it is difficult to have an accurate value for the delay of publication because delays depend upon many factors. From my experience of about 10 years of Chief Editing, the first factor is paper quality: if a paper is short, concise, focussed, nicely illustrated, presenting cutting-edge science, then everybody will want to read it: me, my Assistant, my Associate Editors, reviewers... Such (rare) papers are usually published in less than 2-3 months. The second factor is the fact that the evaluation is made by volunteers (editors, reviewers); while some are rapid, others are not, and here there are very few ways for a Chief Editor to accelerate the evaluation. As a consequence, in the same journal, delays may vary a lot from one paper to another.