I used to tip all the stale premix into our old Panda 4x4. Ran fine. Mind you a Panda would run on camels piss if it had too.
As regards the wifes newer Renault complete with cat, I have tipped in premix before but it was diluted with a tank of neat and the cat tests at the mot's have been spot on.
Stale fuel has not been a problem with the searider, its been used all year round including in the snow.
Searider - The Best 5.4 x Far