I thought I’d mention this as I haven’t seen it on another thread (apologies if I’ve missed it!), but DPReview have a review of the new Tamron 70-210 f/4 that compares it against the new Canon EF 70-200 f/4L IS II with zoomable images at various apertures:
https://www.dpreview.com/reviews/tamron-70-210mm-f4-di-vc-usd-review/3
https://www.dpreview.com/reviews/tamron-70-210mm-f4-di-vc-usd-review/3