TSW's don't come in a wide fitment to really put down a big tire. The widest they make in 5x100 would be 8" Wide which I'd be ok fitting a 245 on but that's maxing the tire out on the width of that wheel.
What you really need is a 9.5 on the back with a 265 to get the meatiest tire on the ground to put down the power, that will be just fine with 300HP. I've got a large selection of wheels that fits your needs checkout either of these threads to see what options we have:
▀▄▀▄▀▄▀▄▀▄▀▄▀ - ******MODBARGAINS ULTIMATE WHEEL GUIDE****** - ▀▄▀▄▀▄▀▄▀▄▀▄▀
ModBargains.com | Forgestar Wheels for your BRZ/FRS - Rotary Forged/Customize Yours!!
That should help out big time!