What are the pros and cons of add on steering verse the full hydraulic steering? I am going to be putting it on a velocity 260

ADD on you are still dealing with the rack helm,,,,, and the cable from the helm to the rack .

How fast is the boat?

I have seen 82 on the gps.

If you are breaking 80 mph, you really need to go to full hydraulic. The add on will only act as a stabilizer to stop some of the play in the drives. As Obnoxus said, you still have a cable that can stretch and break. General rule of thumb is add on for boats over 70 and full hyd for boats over 80. Now, size has a lot to do with it. That is just a general rule of thumb. I would not want a 45' boat that runs 75 with cable steering.
I think you could get away with the add on, but I think you should really have the full hyd. Once you drive a boat with full hyd., you will never go back. Call me if you need some pricing on steering. I pretty much sell them all.
Eddie