I have Hyper 21 4port (Green) and Hyper 21 3port (black)
Although the flywheels are identical (as far as I know) the Black is quicker at mid and top end and feels as if it has more torque than the Green.
I know this is purely luck of the draw with engines but my Black had, and still has, the tightest pinch and great compression. My green was loose right out of the box, which may have something to do with the performance.
Go Black, cheap as chips, loads of spares/upgrades and tough as old boots