it's your money so I'm going to tell you to get the roush motor.
However, if it was my money and I wanted more than the 400hp a stock coyote will put out, I would grab a supercharged coyote out of a local FPV. They make well over 500hp stock and with exhaust, tune, injectors and a bit more boost they are making 550hp at the rear wheels of an fpv, so you do the maths.
They pop up on ebay and gumtree for around 15-17g.
But seeing as this will be a 150k+ plus build, money isn't an issue so get the roush brand new.