of course its possible reliably - my moonstoner 3dr was 400bhp/lbft and that was reliable - as long as the turbo was rebuilt every 18 months.

Inlet was Mountune K2 inlet cam, ported and polished head running motorsport 400 blue injectors.

This was on a harvey gibbs engine - never even had to open it up either and it did a few trackdays and used to love hitting the limiter