Vit E is not a preservative, it's an antioxidant and will extend the life of your product, but not a lot. GSE is controversial as to whether or not it's a preservative. If you search, you'll find that the "chemists" around here don't think so.
My hair likes the more natural products, but preservation is something I take seriously. I'll will use a synthetic preservative. Tinosan or potassium sorbate are newer on the market and considered natural preservatives.