Keep in mind, curse-gaming's Enchantrix works well to give you a ballpark figure, but sometimes it's really far off. A few times I have seen green armor and weapons that supposedly give 100% chance to get a shard. Obviously this isn't true (only blue items give that).
I hate to say it, but thottbot.com will give you very good percentages on disenchants. Look up the material you want, and a list of what disenchants to it is there with pretty accurate %s.