I presently have a single cam bow that is pretty short, has split limbs, and I am shooting off the string, and the thing is very easy to tune and shoot.
When a bow that is typically expected to be "unstable" is, in reality, stable for a shooter then I usually chalk it up to "synergy". In other words sometimes some bows just naturally fit an individual's shooting style, preferences, form, etc.... I had much the same experience with that Havoc. By all rights it should not shoot very accurately for me but for some reason it was the most accurate bow I have ever shot.
All in all, when you put such things aside though, the "usual characteristics" are the most reliable for the average shooter. As for what I personally put stock into.
1. Manufacturing tolerances
2. Brace height (for my form and size this makes the most sense).
3. Axle to axle length
4. Cam Design
5. Overall Bow design
6. Riser Geometry