No, but less variable scans as a general rule.
In other words: could a slow scanning speed produce worse (less exact) results than a faster one ?
There's really no such thing as an "exact" result if you're thinking in terms of some value that is objectively correct for a disc. This is because PIE and PIF are measurements of how the disc and drive interact, and it's meaningless to try to remove the drive from that interaction.
That being said, scanning at slower speeds will tend to produce less variable results on the same drive and between drives of the same type, while scanning at higher speeds tend to magnify differences between drives, between discs, and between scans of the same disc in the same drive.
This makes slower scanning speeds better for comparing your own scans with scans performed by other people in other drives.
For the same exact reason, this makes faster scanning speeds better in terms of discovering problems that might not be seen at slower scanning speeds!
So both fast and slow scanning have their own advantages and disadvantages, but neither is more "exact" than the other in an objective sense.
@raynor: Welcome to CDFreaks!