I'm not trying to be a dick, so don't take this the wrong way. I don't think you'll be able to get 400whp. Even with the standback, I don't think the ecu will let it happen. Good luck on your tuning, but for the time being, I think it would be wise to just tune it to run safely. It'll still be plenty faster and alot over stock, but it's not going to be anywhere near the potential of your set-up. If you have real reputable tuners tuning it anyway, I would think they'd feel more comfortable with a standalone in the first place. One of the best Subaru tuners around the midwest goes by the name Booger, and his claim to fame is standalones. He took a bubble-eye wagon with lots of goodies and a cobb hot-flash, removed the flashed ecu's control (which had the car hitting 620awhp on his dyno as it was), added a standalone (I think a Megasquirt), and tuned it out to 859awhp. That's ******* impressive. At any rate, I'm just suggesting to find out from the builders and tuners what the cost and time would be to switch to a standalone. If it's in your budget, your likely to break some records for this car (as well as some axles, u-joints, driveshafts, diffs, ect...).