With all ofthe replies about just about everything else, did you get a definitive reply that ANSWERED your question about whether to use a Grade 5 or Grade 8 bolt?

If it were me i'd use the strongest grade I could get.

Cheers

Yes, he did. Andy answered it definitively:
Original handlebar clamp bolts are Grade 8
What more do you need to know? He then went on to prove it by arriving at the same answer with different logic:
Grade 5 may be strong enough but for pennies difference I suggest an 8

He and then addressed the Ti question:

I wouldn't use Ti fasteners in a stem but some guys do and many don't die.

To arrive at this answer via different logic: Speedplay/x2 pedals in Titanium say "Not for riders over 175 Lbs". What else do you need to know? Yes I realize that the pedal shaft is a beam whereas the stem bolt is in tension. So what.

That said, I still want a Habanero.

-dkl