Apparently near to 600 BHP:
This has been a series created by CO Mortorsports on YouTube - They took a complete sh*tbox of a Bolf with standard engine, throwing in aftermarket ECU, big turbo & manifold, bigger injectors, better fuel pump, big front mount, with everything else standard - then careful tuning to keep torque from spiking stopping the rods from giving up, dyno graph is supper linear and shallow.
They thought they were done in the previous episode at 440, even took it for a terrifying drive on very snowy Canadian streets.
From the start of the series they were expecting it to grenade - in the episode above they thought there was more power to be found, they seem genuinely confused that it is still holding together after more than 10 dyno runs at over 500.
They are a great channel do lots of Mk5/6 stuff, definitely worth a subscription
Complete playlist for the 18hoopty here:
https://www.youtube.com/playlist?list=PLth4IPq7RyL4T8SQ4q6KBvHA4dpM8ldRY