The NEC ND-3500 is fast ripper of clean SL media, can start at ~6.5X and go up even sometimes to 16X.
You have the same, nothing unusual. Please read more posts, the slow ripping is refereed to DL, and to badly scratched discs.
Now my guess is that if you start DVD Decrypter while the disc in in spin up stage, DVD Decrypter gets some errors and not-ready condition from the drive and slows down.
Again, if you get rip starting at ~6.5X and going to 16X, sorry to burst your bubble, it is normal. Please tell us if you go FASTER than this normal speed, not that you go SLOWER on error situations.