I pulled up my little cheat sheet of select plane weights I made a while back. Not quite 1000lbs, but still about the same as dogfighting with a centerline bomb underneath.
The only thing I can guess is that Gonzo used a heavy guns package on the A-8, making it heavier. [EDIT: This MUST be the case, as the lethality is significantly higher on the A-8 in Gonzo's chart, if they had the same gun package, the lethality would be the same.] Taking the same weapons and fuel packages (2 guns, full internal fuel), the A-8 weighs 9360 lbs, and the F-8 weighs 9849
Just the lighter weight alone will improve top speed and acceleration and turn radius. It would be like flying a 109K4 with 50% fuel vs 100% fuel.
That's been how I feel when I fight in the F-8, anyways. More fuel for the discussion I guess.