I ran a 904 for 5 years in my Dart it ran high tens in a 3440 pounds street car. I had a 450 hp small block with a 200hp N2O kit on it pushing the button right out of the hole. It held up just fine. I did break the snout of the converter once and it was due to my bell housing not being perfectly aligned. Pro Trans in Lancaster Ca has done my transmissions for years and his expertise is second to none. His prices are exceptionally resonable as well.
The 904 is much smaller externally than a 727 as well.
The 904 is much cheaper than the 727 to build in my experience. I dont have proof other than first hand experience in 2 cars I have personally owned that have done extensive track time. My small block Dart picked up .4 and just over 4 mph and my big block Raod Runner with a stock 383 picked up .5 and 4 mph if my memory serves me. Both cars were consistent cars that had the transmissions and restested the next weekend.