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Linux vs Windows tested in 10 games - Linux 17% faster on Average
(video.hardlimit.com)
This is a most excellent place for technology news and articles.
WINE has a FAQ on the matter - https://wiki.winehq.org/FAQ#Is_Wine_an_emulator.3F_There_seems_to_be_disagreement
Short story, it depends what you use WINE for and the perspective you're looking from. I think from a binary's POV that thinks it is calling Windows OS it is emulation.