Obviously I meant to include 4x Spoils of the Vault

. I've edited the first message to reflect this.
but the presence of the 4 Plunge into Darkness sort of craps on my theory. :/
Why? I only expect to cast one tutor per game to win as soon as possible, so Plunges and Spoils are not mutually exclusive. If I could run 8xSotV I would

.
The 60th card, assuming you're going for balls-to-the-wall speed, should almost definatly be Entomb.
Entomb isn't necessarily an obvious choice, as it requires you to have Bazaar in hand. Still, it's difficult to suggest anything else.
Are you counting the Time Walk turn as another turn, in terms of Goldfish speed? I'm leaning towards no as that's what makes sense, but you never know.
Yep, the TW shouldn't count as another turn.