Tony is great guy to deal with. I love my astro T5. If you are making decent power you can go with the A5 that he has that is rated from 450pft-lb & 550hp up to @550lb-ft and 650hp you would need to run a 26spline clutch though. The super high alloy T5 like I'm using is rated @ 350ft-lb & 450hp. They are a very decent tranny, great customer service and the prices are very good. I would recommend them.
The question about all the modified T5's is how long will they last with street driving and an occasional trip to the race track. Some of the super T5's are strip only transmissions and don't work well on the street. So far I cant' remember anyone reporting having 90,000+ miles on one of these super T5's and it is still working great. That's why my choice would be a Tremec 3550, TKO 500 or TKO 600. They are almost unbreakable and will last a very long time. All you have to do is keep the correct lubricant in them and check the oil level every 10.000 miles or so.