The R4s and R6 feel to me like they have noticeable lag compared to the R3 or SL. I haven't used the R8, R9, or R6.2, but I've heard anecdotes that the lag is less with those bodies. I learned to anticipate the R3 lag (which is pretty small) really well during 30 years of almost exclusive use. When using rangefinders, I had to slow down my release a beat to hit my 'mark' in time.
I haven't seen numbers.