A few numbers from my rigs on GPU WU's in the format of mmss(m=minute, s=second).
Start of GPU time|Stop of GPU time|Finished unit time
Edit: Also from other sightings than this. There seems to be some difference in speed between some units and others.
Desktop 2 and 3 are pretty similar here, but 1 is somewhat slower. For laptop it's 1 and 3 that's similar, with 2 being slower.