I don't consider buying it on sale, "jumping the gun" but it definitely depends on your own personal style. For example, if you buy ingredients for Thanksgiving or Christmas dinner 2-3 weeks before you actually prepare the meal, is that too early, or do you want til closer to the date, so that you know for sure all that you are going to fix?
I'd buy it on sale if you find what you like. Then you will have it on hand when you are finished with this top.