Emergency situation - penultimate update

I hated the thought that it might happen, and it happened.
Firm 1 invited me for a second interview that happened yesterday. The results were overall very positive, with a good contact with who would be my future boss and the agency's manager. The job would be interesting, and well, it could be a great job altogether.
They told me they'd discuss it internally and I informed them they had competition from the neighbours. So they didn't waste anymore time and called me with a proposition, with a salary, non-negotiable, and a start date, monday in 10 days. Against their will, I told them I'd hold my decision for 24 hours, to cool down and think it over. The call went off, and I immediately called Firm 2.
Firm 2 called me two days after my first interview with Firm 1 last week. Their departments are more interesting, but I felt like I wasn't the only candidate (two other guys were in the waiting room for interviews when I was there). So I called my contact at this firm, and left a message on his cellphone saying something along the lines of "Firm 1 is offering me a contract, I'd like to know if you want to make a counter proposition". And then I waited.
At 3pm, I had to leave for the code lessons, and forgot to bring my phone. When I came back, after offices closed, there was a message "A position was opened in the Department that deals with this and that, we'd like to discuss it with you".
At that moment, I thought they should have called faster and decided to go with Firm 1. But I didn't call. Now, it's 1:06AM, I'm supposed to be in bed and fast asleep, but I can't.

See:
I've got on one side a firm offer with a salary in 10 days for a position that could be very interesting. On the other side, I've got a half proposition, that could turn sour at any time, but for a position that's a hundred times more interesting (only short of riding the planes themselves actually).
I have said I'd give my decision (that would be positive, I even said) to Firm 1 tomorrow at noon. So in the 3 hours between the offices opening and noon, I'll have to call Firm 2, ask if we could arrange a meeting withing 2 to 3 hours, evaluate the probablility that the position is offered to me and noone else, call Firm 1 and say Yes or No.

Worst case scenario: If I say no to Firm 1 and in the end Firm 2 says no to me, I'll be the biggest ass in the universe.
Bad case scenario: I say yes to Firm 1 and somehow learn Firm 2 was going to offer it to me.
Best case scenario: I say no to Firm 1 and take the offer at Firm 2.

What should I do? Play safe and go for F1, or gamble and try for F2?
I've got approx 8 hours to decide.

Oh, and btw, a firm in Aix en Provence requested an interview to work at Eurocopter in Marignane. The icing on the cake in terms of potential missed opportunities, though I will turn them down, uncertainty factor being close to infinite.