DH20A4P Slow Burn

I just bought this new burner. It burns an 8X dvd at 3:30 and an 16X at 3:00. The drive it replaced a TDK 880N 8X burner burned the same files in at 8X in 3:25.

Shouldn’t a 16X burner burning at 16 X give me better then 30 seconds over an 8X burn?

Used Prodisc, and Ritatek media.