There has been some discussion about taking Force of Will or Spell Snare in my Duress Situation #1 because the Ad Nauseam is "unlikely to fail with 10 life." I posted this on mtgthesource.com detailing a little more about what happens when you Ad Nauseam with your opponent holding Lightning Bolt and Fire/Ice.
First, you need to understand that if you leave your opponent with 5 points of a burn, a good player isn't going to just let you know when to stop. That is, they're going to hold the burn until after you finish resolving Ad Nauseam. This means once you get to 7 life you only have 4 Mystical Tutor + 4 Duress + whatever lands/petals/moxen you haven't drawn that don't autolose you the game. If you go to 6 life and you don't have a Tendrils or a way to find it already (for example, going to 6 from 8 due to Burning Wish or going to 6 from 10 due to Tendrils is fine) you can't win the game because flipping any win condition causes you to go into lethal burn range.
Second, you have to understand that you start the flipping at 13 life, not 15. Your know your first two flips and they are SDT and Brainstorm. You also lose win conditions and gain loss conditions as you continue flipping. At 11 life, Doomsday no longer wins the game. At 10 life, Ill-gotten Gains actively loses you the game. At 9 life, add Tendrils to the list of things that kill you. Doomsday and Cabal Ritual find their way to the list at 8 life. 3 Burning Wish cease being win conditions and begin to kill you at 7 life. Also at 7 life, any remaining Brainstorms, Ponders, Sensei's Divining Tops, and Dark Rituals kill you (putting you at 6 life where you can't flip and win).
When you first start out, you have 40 cards remaining in your deck with 12 win conditions, 13 life, and a grand total of 37 CMC. There are decent odds to win the game here, (you have roughly a 30% chance of winning outright and your alternative is to take a card that that does you, on average, 0.6 damage) but still far worse odds than if your opponent gets to use Force of Will on your Ad Nauseam. There is also still a chance that you 70% chance of not winning keeps stacking until you get into a situation that, in addition to having a decent chance to win, also has a significant chance to immediately lose. As you draw cards that don't win or lose, your average CMC of cards remaining to not kill you is going to rise and/or put you into a situation (with a high CMC like IGG) where you are either losing a lot of potential win conditions (i.e. at 7 or 8 life).
If you take Fire/Ice, you have two major opportunities to bait the opponent (first with a properly played Cabal Ritual, second with Ad Nauseam) into letting you have a guaranteed win. As I mentioned in the article, Force of Will on any card you plan cannot harm you (in fact, causing you to immediately win), so why would you want your opponent to discard it? If you take Spell Snare, you can still bait with Cabal Ritual and Ad Nauseam, but if the Ad Nauseam is let resolve, you now are actually in the same situation as if you took Force of Will: you have to stop early on Ad Nauseam or risk dying to enemy burn.
Taking Fire/Ice gives you the best opportunity to win the game. Not taking it because Fire/Ice isn't as objectively good or "you always take Force of Will" is a pretty poor excuse. Even worse when you lose matches because you refuse to think lines of play through.