Pretty fast, no complaints. The RS render view is instant, which is supernice.
I totally get the 'I like working on a Mac', I'm like that too. Been working on Mac's for over 27 years, so I wasn't happy with apple and their Nvidia dispute. That's the reason it took so long for me to finally switch to a new Mac and a new version of cinema, because it could finally run Redshift in a decent way. Yesterday, after reading this post, I downloaded Cinebench and ran a test.
GPU score: 9292
CPU (multicore): 1961
CPU (single core): 129
But that does get me to a second issue: rendering hair with Redshift. I opened an old scene and converted it for rendering with Redshift, but it kept crashing. So I made a new, very simple scene (because I thought it had to do with the fact that the old scene was well.. old stuff), but it also crashed constantly in that new simple scene.
Unfortunately, I haven't had much spare time lately to really get into it, as learning all the new in and outs are a lot to take in.