The answer is likely to be of limited information value since, even if it can be classified, each implementation is likely to have many variations and subtleties that impact performance materially. E.g., where exactly would you put multi-index query solution in the picture. In fact, not just the structure of the index itself makes major impacts on how the index performs. Caching strategies which help to guarantee index blocks are in memory have a huge impact, as does use of -B2. So, I wouldn't get to wrapped up in labels, but rather look at the whole picture. How well does it do the job?!