Fujinon XF 100-400mm f/4.5-5.6 R LM OIS WR
I shot my last professional motorsports event of the year with this lens on an X-T2 with Vertical Power Booster Grip, and it and the camera body exceeded my expectations. At "working apertures" f/5.6 to f/14, and up to 350 mm, this lens is VERY sharp. Also very fast AF.
Excellent image quality and very fast AF on an X-T2; Excellent reach for sports including motorsports; This lens is MUCH better in every respect, most notably image quality; than the original Canon 100-400 L IS
The only con I can list is it would be nice to be able to lock the zoom at any focal length so the lens barrel does not rack out to full length when I walk from corner to corner ar the racetrack