Those are some really nice features on Sketch. It turns out that it may be the actual best option for teamwork and process optimization.
I've never used Sketch, even because as a Front-end developer, I'm never frequently using design-focused tools like Photoshop all the time (I get Photoshop really well though, and sometimes, not using it regularly feels like a mistake). From all I could see, team performance is great with Sketch. I should definitely see more of it.
Also, nice idea on building El Captain on Windows to use it. The process of changing tools must be really harsh, I'm glad it came to a good conclusion after all :)