A. Neither will do it assuming you mean whp and not crank. If you meant crank, go with the Legacy turbo because it will actually fit.
B. Those 2 turbos are not the same fitment
C. You need far more than you think you do for 450-500 whp. Built motor, built transmission, and a crap load of everything in between. Additionally, nothing about this will make for anything resembling reliability. A WRX making that much would not make a suitable DD. Hopefully you have another car. And a vast budget.
How much are looking to spend said and done? Plan on $30-35k in parts and labor for your goals. You will need to have further funds stashed for when stuff breaks, because it will.