Stock TH400 can handle some power if they are properly prepped but they do have there weaknesses with stock componentry like anything else. Where one may consider them better is that they have a stack-shift strategy where on every shift a new clutch pack is engage without having to disengage or have a timed shift. That makes the shift quality superior over a TF727/904 that always have a timed shift and no matter what, you have to deal with some degree of overlap. This is of course no correlation to overall strength.
Just to note some of the mechanical differences. The TF727 has bigger clutches and can run under significantly lower pressures than a TH400. The stock TH400 intermediate sprag or roller clutch(depending on model year and how it was equipped) is a failure point, even with the better 32 element sprag. The TH400 intermediate band is useless in all performance applications and is often removed defeating any compression braking in 2nd. TH400 and TH727 low reveres band are probably about the same capacity based on surface area,
AG.
I don't buy that they are faster because of the shift sequence, 727 just apply the 2nd gear band to go from 1st to 2nd and it is just a matter of how fast (hard) you want it to shift (unless your running low band apply), good 727s can shift 2nd to 3rd in a matter of milliseconds so even if a TH400 did it slightly faster your not going to be able to tell the difference from that one single shift on a time slip. The engine can be spaced out for a bigger converter, there are some gear ratios available for the 727 so unless you really really need a ratio that is not available then the TH400 isn't really any faster. The only reason I see is if you absolutely need the SFI case and guys with typical 700 HP or less don't need it.
I slept at a holiday in once upon a time so I definitely know what I am talking about.
