I have no idea the answer to Question 1 because we haven't had an OIS since switching (knocks on wood).
The answer to Question 2 is that proper training with the optic (a really big deal) equates to a big improvement in score.
We don't force anyone to carry an optic, but about 85% of the department now chooses to. Our department wide qual course starts at the 25 yard line, moves up to the 15, then the 10, then the 7, and ends with point shooting at 3 yards. You get three consecutive tries to pass. If you fail all three you get benched (taken out of patrol or your assignment), put on a PIP and sent to remediation. Typically we have at least a couple people a year make it to a PIP.
Since we started issuing the optic, I have only had two people not pass on their first attempt at the qual. The two that didn't easily passed on try #2. Nobody has made it to try #3. Nobody has been put on a PIP.
Our SWAT pistol qualification course is much harder than the patrol one. It historically has been used to weed people out in the selection process. The SWAT guys are now complaining that their pistol course is too easy and that with optics everyone can pass it.
We call that a clue.