^I didn't check all 6 possibilities, but I checked a few, and they add up to 100%, so you're fine. The formula is correct.
Yes, 60% is always a better outcome in a similar way to that, especially if you have a good amount of slots, like the 6 that you have.
Question is whether you feel confident enough and have enough mesos to deal with the (fairly small, but 1 in 5 chance) risks. It's nothing like exploding it, though. Honestly, if I were you, I'd feel quite happy just to have the helm as it is (didn't you say it only took 2 runs worth of helms?), and consider the last 6 slots a bonus. =)
Yes, 60% is always a better outcome in a similar way to that, especially if you have a good amount of slots, like the 6 that you have.
Question is whether you feel confident enough and have enough mesos to deal with the (fairly small, but 1 in 5 chance) risks. It's nothing like exploding it, though. Honestly, if I were you, I'd feel quite happy just to have the helm as it is (didn't you say it only took 2 runs worth of helms?), and consider the last 6 slots a bonus. =)