tccoa has a wealth of knowledge..
Yes, the 99- up 4r70w's are built alittle better ( better internals) then the older AODE's ( atleast the early 94's).
You can beef up the trans you have though, it just might end up to be more expensive.
And im sure you know, the 4R70w from a V8 mustang, will NOT work on your 5.0..
You would have to work from your current AODE's case, and build it up, or pick up a 99-up 4r70w from a v6 mustang.