What I remember reading about the impact of speed limits is that reducing them only affects the slowest quartile or so of drivers while changes to road design such as reducing road width and visibility slow down almost all drivers. Reducing the speed of some drivers and not others increases aggressive driving and probably isn't good for safety.
I don't take the position that reducing speed is a good answer for every high-risk road situation, but for those where it is, changing the speed limit alone is likely a poor solution.