A lot of builders prefer the quench pad in the gsr head over the b16, but then a lot also prefer the port arrangement of the b16, which apparently Honda did, as well, choosing it for the Type R.
The pad is the flat area of the chamber on either side of the valves, which match up the the flats on top the piston.
When fuel and air is compressed on the compression stroke, the two flats comes together very closely, forcing the fuel mixture to the center of the combustion chamber (atomizing and mixing just that much more) where it is closer to the spark plug and thus igniting it faster and more completely.
It's the design on Honda heads that makes them so effecient and the reason why we can run 12:1 or better on pump gas.
The gsr head is a little different in that the pads are not recessed into the head like on the B16. There is still plenty of quench on a b16 so in practice, I'm not sure it makes a lot of difference, unless you building something to meet a certain criteria.