This pics was for a chipset block but a friend has realized the same (an evo of a previous block) but no testing..
He was the first to use this design but his block is better (barbs are different than you and no pressure drop for barbs because not 2 x 90° barbs). Have a look here :
http://www.overclockers.com/tips247/
Personnaly, I won't make gaps into fins because it will destroy the flow without give anything better, your divets are good enough to improve thermal coefficient on the baseplate..(and flow is already turbulent (Re high with flow speed).