upgraded ct-26 with a 57trim?

Does anyone have information or maps on this upgrade? I heard that it will be able to handle around 450hp?

Sorry but no. The 57 trim is one of the worst upgrade options for the MR2. Most turbo manufacturers describe it as too close to the surge line. As far as real dyno tests from CT26 upgrades try here:
http://www.atsracing.net/ats_ct26_turbocharger_upgrade.htm
and here:
http://turboforum.net/dyno/pages/ct2646.htm
http://turboforum.net/dyno/pages/ct2650.htm
http://turboforum.net/dyno/pages/ct2654.htm

ATS is working on a new CT26 upgrade that will produce near 360 flyhweel hp. Check our website www.atsracing.net in ~2 weeks for dyno results.

Aaron

So does that hurt performance or just make it less reliable?

Also, what size would you recommend for upgrading the ct-26? Goal of around 300-350rwhp.

You can't get 300 rwhp with a CT26 upgrade. Period.

For 300-380 rwhop we recommend:
http://atsracing.net/ats_racing_td06_turbocharger_kit.htm

They dyno graphs posted are on a car with stock ECU, stock cams, stock head, stock displacement, stock b-pipe etc. We wanted to illistrate how much power the turbo kit made on its own.

Aaron