aguila makes a 60gr subsonic called subsonic sniper, but they dont have any more power than u have now.
the only thing better than stingers that ive used are the Velocitors. they also have a much better hollow point with a poly filled tip. i think they are 40gr at 1400fps the stingers are 32gr at 1600, but i never got better than 1540 on the chrony.
i just shoot rem subsonics anymore because they are nice with a silencer.....
they also open up better because they are soft lead. they wont exit a cat... but they sure make a mess inside