The company has grown at__________ pace, doubling in size from a year ago and pushing international competitors aside.

Meteoric is the right answer.
The statement implies that the company's expansion has been quick/fast/swift.
The word that completes the statement correctly is option 'meteoric,' which denotes a quick rise.
Supernumerary means more than the required number.
Histrionic refers to being too dramatic.
Eroded means to wear away.