If you have even a partially collapsed catalytic converter, then the power of your car can be on a massive downward slide. In fact, in most cases the prob is pretty obvious to say the least.
A visual check for a melted or restricted CAT is your best warning. If this is the case, then try and pick up a cheap factory catalytic converter from an importer or from me, with the bonus being it will more than than likely work better in terms of protecting the environment than the cheap compliance CAT that's currently installed on your ride
