I bought this lens, along with the RF 24mm F1.4 to carry out a back to back test. To cut a long story short, I ended up keeping this lens and returning the F1.4, reason being, the image quality difference was not sufficient to warrant the significant price difference.
The F1.4 image quality is superior - but not by a lot (my opinion from real life testing). The Image Stabilisation on the F1.8 is also a bonus.