I can tell you my experience. My stock T-45 lasted for 200 passes on the dragstrip at the 400+ rwhp level. I was so impressed that I got it rebuilt locally, using stock components. The rebuilt unit lasted 20 passes. Tried a rebuilt T-45 from Promotion Powertrain, that was beefed up to handle 700 HP. I had problems with it from day 1, and told them about it. They did nothing about it, and wouldnt stand behind their product. The tranny lasted less than a year with about 20-25 passes on it.
Needless to say, I don't have any good things to say about rebuilt transmissions although I am sure there are people who had good luck with them.