I think, perhaps, mirrors is not the appropriate description for a range of cameras anymore.

I'd match the performance of my A77 & A65 against any aps-c dslr anyway, including focus sharpness and 12 fps performance. I doubt they're in the same category as the 4/3rds systems some have, although on a technicality, they have translucent mirrors not reflex mirrors.

I'm also very happy with my A7r, completely mirrorsless and full frame.

At this end of the gear spectrum performance is more likely to be about users ability than gear.