High baseline

Now after fun and cool experience optimizing customer's code with a low baseline, I am struggling with a code with a high baseline. It had been optimized for many years by different engineers from different companies, and all I can find are a handful of potential optimizations that bring ~1% each, making code complicated (well into "red zone" in Shipilev's terms).

The only interesting option is to try an approach from a research paper recently published by my colleague. (Thank you very much R!)