It depends on the frame as much as the crank. I ran 3 sets of them with 107, 110 and 115mm on differing bikes, 107 is for frames with narrow profile chainstays and less tyre clearance. My Pace Rc200 with standard Lo pro cranks (Turbines, M735 on, Sugino, Middleburn RS3 on), uses a 107mm as they have Assymetric chainstays, Ritchey frames typically use narrow BB/s Alloy frames would need a 113 or 115, what frame is it for?
In many cases it's trial and error with different cranks on different frames, there is no hard and fast rule unfortunately.
To make matters worse, Syncros had 4 different end cap profiles and some have a concave shape and give less crank clearance than others. I would try some Shimano ones to start with before committing to a Ti one.