You will have to play with locking it up to see where you car likes it the most. I locked mine up at the starting line. Doing this, makes it lock when it shifts in to 2nd gear. It will not lock in 1st.
My car picked up .15 and 2 mph in the 1/8 mile locking the converter.
Not sure about how long the converter can handle it.
My tranny is now slipping but I don't think it had anything to do with locking
the converter. It was going out anyway.
Some people lock up once in second and I've heard of people locking it once in third. It's up to you.