I think this position presented calls for defense on any equipment. The combo can't be made at soft speed, and the cue ball will likely run into the six ball, which complicates the shape onto the one. In addition, moving the six may tie something else up or leave the six in an unfavorable position. To that, I'll add that the final position of the one is not that predictable, as the thickness of the hit on the five, even assuming the combo is made, cannot be judged with 100% precision. Even if you make the combo, the one will often end up on the bottom rail. Too many variables for my taste. In my view, the safety you played, if executed, produces a win far more often than the combo.
If the combo were the one-nine, rather than the one-five, I'd play the combo, concurring with Chris that your chances of making it are pretty good.