I think the boss is a forged engine which would handle turbos better for more boost. But hell you can get a 5.0 slap a sc on it and be around 550 ish under low boost . I'm sure others will chime in. But there is a twin turbo 5.0 running 9.4 1/4 miles I think like 750hp
The Boss has the forged internals and would be the choice I would make.
15 F22 M235i, JB4 Stage II, Cat delete, CAI
12 GT Prem 5.0 (Sold)