We had a large collection of 1-Gig JAZ disks which we are gradually transferring to CDs. Urge you to do the same if the stored data on those Zips is unique, irreplaceable, highly important, etc.
The DVD speed is only an issue of you are thinking of frequent access. Most archives are drawn on between once and twice over years. It's a tardeoff. Maybe the OSX access time is less, I don't know.