When it comes to cutting things, my first targets were:

1. Emrakul (not tutorable) when you can cast him you should have already won. I tested him alot in the last days and found out, that i can almost never cast him anyways. When i could, i could have also won with Sigil in 2-3 safe turns.

2. Crop Rotation / Enlightened Tutor. As being said, its card disadvantage. Tutoring things is flexible (which i think is important) but this deck can live with 1x Enlightened Tutor just fine. It couldnt with only 1x GSZ. At least in my list i'm not running that much Silver Bullets to justify 2x Instant-Tutor

btw.: I really changed my mind about your GSZ-Plan. I tested it extensively in the last days too, and i think it gives alot of consitency. You are right - with GSZ many more hands become keepable. I will be running 2 myself.