If you are a UK scholar, or seeking employment in the UK, you will need to pay some minimal attention to the REF (the Research Excellence Framework, the current name for the periodic assessment of academic research undertaken by the UK funding bodies). The rules of the REF change from cycle to cycle, but the bottom line is: if you are publishing high-quality research with reasonable regularity, then you are doing all you need to be doing, so far as the publication portion of the REF is concerned. All publishing formats are eligible for submission to the REF.
It does not matter whether your research appears in a journal (still less a ‘highly-rated’ journal) or in a collection of essays or in a monograph or online. When your research is assessed by the REF panel, it will be read in full by an assessor, who will make a judgement based on what is read, not where it appeared. (You will be told otherwise – perhaps by managers, or scholars in other fields, where practices differ – but the truth is that all history publications submitted to the REF are read by assessors and judged on that basis alone).
Therefore, all that matters is the quality of what you produce. We are not always the best judges of the quality of our own work. So peer-review is a helpful guide to the REF outcome (which is simply peer-review itself). That is why submitting to a ‘highly-rated’ journal is a good idea – because your work will get searching peer review and acceptance in a competition is itself an indicator of quality. But a first-rate chapter in a book will still get equal treatment by the REF panel.
As we say above in the section on book chapters, peer review tends not to be so rigorous for collections of essays. In addition, editors of collections often try to pack too many items into a single book – to please more colleagues! – and so you may be confined to 6-8,000 words whereas a journal article may run to 8-10,000 words; and you are likely to be able to say more, to demonstrate more rigour, significance and originality in a journal article, than in a short book chapter. This is also the reason why books tend to do better in the REF – not because they are favoured on principle, but because historians tend to put their best work into their books, at the length needed to demonstrate the depth of the research and the validity of the argument.