Remarkably quick mice tore about (8)
I believe the answer is:
meteoric
'remarkably quick' is the definition.
(I've seen this before)
'mice tore about' is the wordplay.
'about' indicates anagramming the letters.
'mice'+'tore'='micetore'
'micetore' is an anagram of 'METEORIC'.
(Other definitions for meteoric that I've seen before include "Swift - spectacular" , "Of a shooting star; remarkably fast" , "Spectacular sort of rise" , "Spectacularly fast" , "Brilliant, as a shooting star" .)