I haven't heard of a single EF lens not performing identically on R. I had about 15 EF lenses when I first got my R and never notice any image quality issue or slow autofocus etc. The EF's I still want to keep shooting on my R are the 135/2, 180/3.5 and 600/4IS. These three stand out because 1) they're the two sharpest black lenses (all the telephoto whites are sharp), 2) the lens formula's back glass is nowhere near the lens mount, causing me to assume that even if/when an RF version comes out it won't be improved by the new-found freedom to get much closer to the sensor, unlike the wide-angles and standard zooms.The EF 100mm has so many good reviews, I was curious about how it performs on the R (or R5).
However, with the exception of these 135mm+ telephotos, I think ALL the RF lenses are going to be far superior to the EF counterparts, and I'd advise to wait for a native RF version. (Example: RF 50/1.2 literally 10x sharper than EF; RF24-105/2IS far smaller than EF MkII while sharper than EF MkI; IS can be better coordinated with body thx to higher bandwidth communication; shorter flange-sensor distance allows sharper and smaller wide-angles.)
I could recommend the EF 180/3.5 Macro as being extremely cheap second-hand considering how good the image quality is. If you bought used, you may be able to sell used for about what you paid if/when a native 100/2Macro comes out. On the other hand, I've never really used the 180 for general purpose shooting (eg, portraits) in part due to size and in part due to AF speed. When I eBay stuff I'll put the 180 on the camera and shoot all the product shots with it, macro and non-macro, but that's the only time I use it non-macro.