We (rsync.net) do not have any numbers, but we know what happened when we broke 85% on a zpool that contained a single vdev ... things went to shit.  Luckily, we expanded that zpool with two other vdevs and it <i>sort of</i> balanced things out and rescued it ... meaning, enough IO happens on the other two vdevs to make the zpool viable.<p>However, the effects scared us enough such that we will <i>never let it happen again</i> ... and that is a fairly severe economic and provisioning penalty (ie., chop off 15% of your inventory <i>on top of</i> the three drives per vdev you already lost for parity).