Share rating at upper limit? That's annoying (5)
I believe the answer is:
pesky
'annoying' is the definition.
(I know that annoying can be written as pesky)
'share rating at upper limit?' is the wordplay.
'share rating' becomes 'PE' (as in P/E, priceearnings ratio).
'at' says to put letters next to each other.
'upper limit?' becomes 'sky' ('the sky's the limit!').
'pe'+'sky'='PESKY'
'that's' is the link.
(Other definitions for pesky that I've seen before include "Annoying - troublesome" , "Bothersome" , "Annoying (informal)" .)