Unusually big (6)
(Other definitions for bumper that I've seen before include "kind of car" , "First casualty in car crash" , "Something big" , "large drink" , "Glass filled to brim" .)
(Other definitions for immense that I've seen before include "Unusually great in size" , "Huge, vast" , "Vast or enormous" , "Extremely large or great" , "Unusually large or great" .)
(Another definition for oversized that I've seen is " bulkier than usual".)