It is most likely a function of the quality of the disc. OC-Freak, when testing burn quality, likes to get the disc to read at the full 16x, and then if the drive thrashes at the end, then he knows that the burn didn’t come out as well.
Take a look at the thread for the 48161H (the 48x combo) (see my sig) and see the scans that I posted. My +R burns turned out very nicely, and they read well at 14x CAV. My -R burns didn’t go as well mostly because my -R media isn’t great and my drive doesn’t burn -R as well as +R, so you can see the thrashing effect towards the end.
In the original firmware, if you read that disc, it won’t go crazy at the end like it did for you, but then again, at the end, it’ll be reading at a max of only 8x.
Using this patched firmware is really your decision. If you want higher reading speeds (8x CAV is pretty slow), it will come at the price of possibly thrashing at the end of the disc. If your media and burns are good, then it’s easy to pick the higher speed. If your media & burns are not as good, then you’ll have to make a decision regarding using the higher speed or using a lower speed.
If you look in the 166S readspeed thread, you’ll see something similar… where some discs read smoothly while some go crazy towards the end. It’s a function of burn quality…