I am running a stock STI 2.5 liter short block with my 04 WRX 2.0 liter heads with 1.5mm Cosworth head gaskets and have been for about five years now. I have gone though two gear boxes now and I'm only making 310whp and 319 lb ft of torque on a TD06 18G. I finally went with PPG straight cut gears with the STI RA 5th. The 5th gear was left over from the first rebuild which was the STI RA 5 speed.....it lasted about six months. I have had no problems with the PPG gear box so far, I am sure if I upgraded again power wise the box would not last. So if you are going for 400whp budget some money for the STI 6 speed it will save you money in the long run. Side note I would like to know what was meant by deshrouding the heads?