Yes they are strong, a buddy has a 5.3 with a T75 single turbo, on a low buck build, it just stays together, it made 699 at the rear wheels on the local dyno. Another buddy has a stroked BBC with twin T75's, it made 702 rear wheel on the same dyno.
The limiting factor is the fuel injection, it costs big bucks to upgrade from where they are now.
One is running FI-tech, the other Holley Sniper.
Both are running low boost, under 10 psi, they are still like ice-skates on the street without slicks.
