^^^ I think he's referring to Spock's statement from TWOK when he said "they can outrun us, and outgun us", which was perhaps due to Enterprise's heavily disabled state after their first engagement with Reliant (unless there was some other reference I missed). This may not always be the case with two such vessels running at 100%.
As far as speed is concerned, they both seem relatively identical, although the Miranda may have less mass overall, making it slightly more maneuverable. As far as weaponry is concerned, the Miranda does seem to have a distinct advantage over a Connie with their mega phaser emplacements on the roll bar, plus two rear facing torpedo tubes, neither of which the Connie seems to have. It could be argued that a Miranda is more heavily armed.