I believe this to be normal.
Scanning pressed DVDs will always show PI Errors, so they cannot be assumed to be perfect even if there are no scratches visible.
Also, the drive is now reading near the limits of its capability, so there will be more occasions where it will slow down to try and resolve what it might consider to be a marginal burn.
In general, I wouldn't worry too much about it unless the symptoms become worse. And even then, you can always flash back to the stock firmware if you feel that your drive does not work well at this higher reading speed.