DVD Write and read speeds

Single Layer(4.7GB) write speeds
1x (CLV) = about 58 minutes
2x (CLV) = about 29 minutes
2.4x (CLV) = about 24 minutes
4x (CLV) = about 14.5 minutes
6x (CLV/ZCLV) = about 10-12 minutes
8x (PCAV/ZCLV) = about 8-10 minutes
12x (PCAV/ZCLV) = about 6.5-7.5 minutes
16x (CAV/ZCLV) = about 6-7 minutes

Dual/Double Layer(8.5GB) write speeds
1x CLV = about 105 minutes
2.4x CLV = about 44 minutes
4x CLV = about 27 minutes

Single Layer (4.7GB) read speeds
6x CAV (avg. ~4x) read speed is max 7.93MB/s = ~14 minutes
8x CAV (avg. ~6x) read speed is max 10.57MB/s = ~10 minutes
12x CAV (avg. ~8x) read speed is max 15.85MB/s = ~7 minutes
16x CAV (avg. ~12x) read speed is max 21.13MB/s = ~5 minutes

* write speed time and read speed time is not the same because writing requires some extra steps and also does the faster writing above 6x usually use lower write speeds for some parts of the dvd. 4x DVD speed = 36x CD speed. See section 4.2 in the DVDDemystified FAQ here.