My mechanic feels I will get more pep or off the line performance by by having the torque converter rebuilt with a higher pounds opposed to going from 3.23 to 3.91 gears in the rear end.
Using your first sentence I would say converter as well. It will allow you to "launch" quicker. As far as pulling you probably won't notice a whole bunch of difference.
And it really would help to know more about the engine, stock? cam? headers? etc. It all adds up.