The 70 would have been better like its superior rendering of the sound mix, but not quite as good as a perfectly projected IB print.
I think an IB would have blown the 70mm away in terms of picture quality… But the larger format does have an advantage in terms of lumens and screen size. The larger screen you have, the more light you need to push through the film to get it to light up the screen. There’s only so much light you can squeeze through a 35mm frame before you end up melting the film. 70mm is able to ‘dissipate’ the heat so to speak, and uses a larger surface area, so you can get a brighter image on a larger screen.