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Performance wise the 3.42s and the 2800 stall T/C will give you a MUCH BIGGER performance boost especially if you have 2.73 gears. If you have not already bought your T/C you might want to consider a converter with a bit more stall between 3200 to 3500 stall. You did not mention which 2800 stall converter you were considering. If you are thinking about the Vigilante 2800 that is an excellent choice since it really stalls at 3200 RPM.
I would not install an underdrive pulley if I was not also going to install a new cam at the same time. Installing an underdrive pulley by itself involves too much work for too little gain.