the rod to stroke ratio is better in the DOHC engines which yeilds higher revs. Next, when you adjust the cam timing, you can retard one and advance the other cam where as in the SOHC engines, you either retard both, advance both, or just buy a new cam if you want a combination. Finally, out of the box, honda designed the SOHC engines as economy engines where the DOHC engines are there performance models. So as calesta said, the cams are more agressive, fuel maps are better, and the pistons are higher compression.
Next, tannys for the sohc engines suck. They have long gears, dont last a long time and grind like crazy. The big reason why I dont want to do a big NA build up on my d16z6 is because the trannys break fast (even though they are a dime a dozen compared to ITR and GSR trannys)