I don't believe that that kit has been released yet, but it will definitly be the highest output system for the celica as they are planning on reinforcing the internals (~300 whp)
of course, any FI system can be made crazy better by getting new internals from www.monkeywrenchracing.com
and increasing boost
The only kit that is now available for the GTS is the turbo performance kit, but there have been a lot of problems with customer service and bad parts with that kit.. as well as some issues with leaking at high temperatures
The infamous TRD
kit would prolly only be for the GT, but chances are it won't ever happen.
Blitz has a supercharger kit for the GTS that will be available any day now if it isn't already. It is kinda pricy though at $5000 for ~210 whp
Alpine Developments is planning on releasing a supercharger kit for the GTS around march of next year.. they are expecting to see similiar numbers to the blitz kit for ~$3000, but that remains to be seen
hope that helped...