A well worked OEM Casting cylinder head with proper porting and cams will make the exact same power ...
The extra $$$ spent on a DART cylinder head would be well spent somewhere else ... After seeing both I belive the OEM unit has better fit a finish and smoother castings than the DART product anyway
I doubt the 'average' honda enthusiast would benefit from the head much at all really.
A well worked DART cylinder head with proper porting and cams would make more power...
...but, in an extensive build, i believe it would make a difference.