I haven't used their 8" speakers but if I needed one I would look at Weber speakers! Have used a few of their 12" and their Weber signature series are what come stock on some fender champ reissues. The signature series has a bonus of being inexpensive! The Chicago series is American Jensen/Oxford style replacement speakers and are what I would look at personally. Good luck!
Also nearly anything you get will likely sound better than the Celestion super 8. The super series are bottom of the line Celestion and are very cheap things made just to have a "Celestion" label on a functioning speaker in the unit so, yeah anything should be an upgrade!