Chrysler did a lot of testing back in the mid-'70s between a 727 and 904 in Stock and/or Super Stock small block combos. With both versions built to the same degree with matching converters, the 904 was an average of .15 faster than a 727.

I footbrake a JW Trans. 904 with good bands and clutches, a reverse manual valve body, 4.2 lever and 2.71 low gear. No aftermarket billet or aluminum stuff or roller bearings. Works great, no problems and excellent wear characteristics with Amsoil Supershift fluid. Best of 1.47 60' with 11.31 @ 115 time weighing 3,540+. Built right, they are a very durable trans and you'd have to spend a LOT to just try and get an extra .15 out of a 727.

You probably don't need a 2.71 low gear and, in theory, a high torque engine will see less difference between a 727 and 904. But a 727 should last longer and be more durable.