With the goal of use both buttons for many FG think I will put these buttons together with the six buttons layout(vewlix at the moment). Until where I know these games make useful use of both.
KoF 2k arcade: strike gauge; SFA2/3 arcade: some specials and super combos; Samurai Shodown IV, V: suicide; CvS2 some Dan moves.
SFIV console(PC too?) series: S/BLink; SFAA: same above.