I own a '18 Street Triple R and love it! I love the new metal flake in the gray paint on the 2020 RS. As you compare models - it's great that the new 2020 Street Triple R get the facelift, new daytime running lights, and up/down quickshifter (all at a lower price), but they've now done away with the TFT dash on the 2020 Street Triple R! The TFT is a game changer and after riding with it I couldn't imagine going back. Unless you must have a 2020, maybe consider 2019 models? There seems to be a consensus on this forum that the TFT graphics are better from 2017-2019, and the increased mid-range torque on the 2020 RS might not be enough to push you in that direction.. Give and takes.
Good luck with negotiations!