Forgive me for the crazy response but I just have to ask - Is it not fast enough??
Our 93 in stock form, with a tick in the valvetrain, has more than enough power to do anything we ask. From what info I have read, there isn't much in the form of upgrades that can be done other than turbocharging. I own a Turbo Buick and it has more power than most can handle...and it's basically stock. I rarely go WOT because I don't see the need. On top of that, it isn't running very well. I personally don't see any need to do any upgrades to the SC. Lexus built it as good as they could right from the start. 225Hp ain't too shabby!
That being said, a torque converter with a higher stahl will appear to give you more power as it allows the engine to rev up and reach it's power band faster. Probably the best bang for the buck.