T5 guys are still using Dextron/Mercon so I'd have to think that the Synchromesh is still recommende for the 3550/TKO.
There's only two place that I know making Proshifted components...Liberty and Hanlon. Other shops may offer the assembly/installation, but I'm pretty sure that only Libery and Hanlon make the gearsets. I checked on proshifting my T5 last year and the cost was about $600 for the components from Liberty (less rebuild kit). So if you're not into T5 rebuilds yourself, you're also going to have to pay somebody to do the rebuild.
The torque capability of the tranny isn't increased any, but it allows the driver to make much cleaner shifts and hence extends the life of the tranny.
------------------
Jeff Chambers
Trophy Stock #3
11.462 Seconds / 117.43 MPH
Chambers Racing Team