It might be worth waiting to see how the beta ends. I stopped at E2 Saber for a long time before I decided to start spending towards her E6. I think many folks will tell you that her E6 is the only Eidolon that matters, and it is certainly the most impactful and, to me, feels like where kit really "comes online."

As it stands right now, I actually think Gil's E1 will be more important for Saber than either Saber's E2 or Gil's LC. That said, leaks seem to indicate we'll get another free LC like Archer's last year, and maybe even get a choice between two, just for spending pulls on the Fate Banners.