Thanks for adding the "Rest of the Story" It is real hard for people to answer a question when someone dosen't tell everything up front.
If you tie a lot of flies buy the whole saddle. You sure can't lose anything by doing so. If you buy it and you figure you have to much post here and see if someone will trade you for half or quarter of another color. Hackle never goes to waste unless the bugs get it.
I am just guessing here but a half of a whiting saddle will tie in the neighbor hood of 1200 flies. That is just a guess on my part but I bet it is short. You tie that much? If so buy the whole saddle.

You can still size your hackle the same way as I gave above no matter the length of the shank of the hook. Ron