Yes, of course. First of all, I just updated it to 0.15-0.20. This might actually be a bit high, but I've set it higher than what I feel is right due to my bias (consisting of Eliezer finding a more interesting way of writing the story).

It is "so low" due to the following:

• a) I believe that Quirrel is not seeking a physical confrontation with Harry (earlier we saw him toss Harry a knut (that could have been a portkey to a volcano))

• a.1.) Harry wouldn't win such a confrontation (a sneak attack would of course be much more likely to get the job done)

• a.2.) If there is a confrontation and if that confrontation ends with the death of Quirrel, I expect the wands or Lily's ritual to be the deciding factor, not any action of Harry's.

• b) I consider it most probable that Quirrel tries to turn Harry to his ways (0.6 < p < 0.5)

• b.1) Harry might try to counter-turn Quirrel. I do doubt though that this will end with one of them dying. Killing one another seems so irrational...

• c) if Harry decides Quirrel must die, he'd do better using henchmen

[I'm now officially not a fan of the editing options here]