I got some experience with ESS twinscrew.
Stage 1 on M54B25 pulled 243whp on mustang dyno (would have been around 250 on Dynojet). That car was real fun to drive. Instant throttle response, flat torque curve.
I still think it's better option than messing with NA (mostly gains in the high RPMs) and nitrous (damn, my tank is empty again!)