Am I blind but the first post in thread doesn't say any workshop names? :S
I'd recommend MRT in Rhodes, Sydney. The owner (Brett) drives an Evo X and his company seem very specialised in Subies/Mitsus, and more importantly the 4B11T and SST. When I was picking my Evo X up the other day, there was a RA owner there and we were comparing the graphs of before/after the custom tunes.
My recommendation to you Gas is to get some bolt on parts before you do your custom tune. Get yourself an exhaust and an intake, then you'll get a lot more out of the tune. Yes it'll void warranty but in theory so does everything else when it comes to parts which are directly impacted by your mods.
If you're trying to get some kind of assurance/warranty, I paid the MRT premium because I feel they are very accountable for their work but to each their own.
ps. If you're interested in my tune on my Evo, feel free to check out my thread:
http://clubcj.net/viewtopic.php?t=7686