The one thing I didnt see anyone ask is, how well can you drive a 4 gear? And do you have nitrous?
It really depends on the driver first and then the car, you can have the best of everything and set up perfectly, but if you cant drive a 4 gear you will launch the engine. Especially if you have nitrous and miss a shift.
As far as the question at hand, are we talking a stock suspension or a chassis car? You have to set up the car so the engine, trans, rearend and suspension all work together. If you are trying to compare the same car with a 4 gear or an auto, you are comparing apples to oranges not apples to apples. Things like your cam, carb, timing, shocks, suspension and more need to be matched to the tranny you are going to run.
You need to choose which ever one you are comfortable with and be honest with your self about your abilities. You will get just as many people that say the auto is faster as you will that say the 4 gear is faster, it all depends on the driver and weather or not your car is set up correctly.
Ive always been a fan of the 4 gear. Back in the 80s we were lucky enough to have a place where we could street race without getting hassled. We had a three lane road with the 1320 permanently marked on the road. My car wasnt that fast, mid to upper 12s but for an 18-21 year old kid it was fast enough and I could out shift a lot of the guys and there autos but it took a lot of practice to shift that fast.
Oh yea, I have a 4 gear in my blown 65, and I did see a few people say the 4 gear is lighter, this is not necessarily true. Im not sure about the 904 but if you take the A-833, a good clutch, scatter shield, flywheel, clutch linkage and shifter, and compare it to your 727, torq converter, flex plate, shifter and cooler. You will find the auto is a lot lighter. My scatter shield alone is about 100 pounds or more, not to mention the cast iron A-833 and flywheel. I didnt built my car for the track though or I would have done a lot of things differently.