It depends how you define 16x.
The average Joe could think that it means 16x over the whole disc - this would mean a burning time of around 4.00 mins.
However, the marketing men have got at the definition, and twisted it to mean 16x at some part of the disc - which usually means the end. Pioneer even conceded that the 108 burned faster at 12x than 16x! However, I believe newer firmware has improved this.
Currently 16x speed means a whole dvd will be burned in ~ 6.00. The LG 4163 is the fastest (at the moment) in ~ 5.30 mins. My NEC 3500 does it in ~5.40 mins. The Pioneer 108 is nearer to 7.00 mins, which is 12x (average) burning speed.