Depends on cam profile but especially with the JUN cams, starting from 264 (10,8mm lift), to 272 (11,0mm lift) upto 280 (11,5mm lift) degree duration cams HP and torque gains are very evident. This will be more useful on allready tuned engines. HP gains upto 30-40HP can be achieved in top rpm range. But all very much depends on turbo spec, boost pressure and other tuning factors.
The Tomei cams are more "friendly" and less "racy" than the JUN cams; Tomei cams deliver more over-all HP and torque gains, whereas JUN cams are more agressive in profile and love to be wind up in the rpm range. With 264 degree and up JUN cams heavier double valve-springs will be needed. Also when changing cams plaese note if the surface of the rocker arms are still in good shape; these need to be scratch free, otherwise these beautiful cams will be killed in short while.