Unsure as to how powerful they were, but both 4488 and 3663 had issues with boulders rebounding out of the tower after their shots at their first events.
if you really want the kings of ridiculously hard shots, gotta go back to 2013
the robot I remember best from that is 3711; this video shows it relatively well at the 40 second mark, but you kinda had to be there. when they shot, you
felt it;
http://www.thebluealliance.com/match/2013wase2_sf2m1