The Toyo T1R has a softer sidewall than the RE030, but I can't say exactly what the effect would be. It wouldn't make it feel stiffer, but is a better tyre than the RE030.
On mine after damaging a sidewall I 'borrowed' a set of RE040's from my wife's RX8. The RE040's have much more grip than the RE030's, but below about 6 degrees C they feel like wagon wheels. They are also very prone to tramlining. They feel fine on the RX8 though - different suspension tuning. They feel stiffer than the RE030 - the difference was quite noticeable as soon as I put them on, and it improved the turn-in considerably. However, RE040's are also noisier, heavier and 'harsher'.
If you go to 235/40-18 the choices open up a lot, they would be very close to the rear strut but should fit. This means that F1 GS-D3, Michelin PS2 and so on are all available to you. If you want to stay on 225/40 the RE050 might be a good choice.
(Interestingly I ditched the RE030's simply because it wasn't feasible to get a replacement easily. Anyone with a FSTi who plans to keep the OEM RE030's might eventually need a spare one, so instead of selling all 4 of yours you might find that it is more likely that the demand is for single ones. Depends if you've got room to store them I suppose !)
PS. The RE040's are still on the car - the RX8 got a new set !