Typically things that will make the kart turn-in better will conversely hurt your exit. This is because inducing better turn-in requires quicker inside rear lifting action and therefore also quicker set-down of the inside rear after turn-in. This results in a flat kart on exit, giving you a bog.
Hopping results from too much lifting action too quickly. So your narrower rear track width might help the kart keep the inside rear wheel off the ground more easily, but would have increased the amount of hopping you were feeling if you narrowed it too much. In a fast corner, you have more force on the rear wheels so you can overload them more easily and get a hop.
My suggestion would be to split the difference on the rear track width to 54.75″. I’d also recommend a little negative camber. For me it usually helps the kart point into the corner and carry the inside wheel longer through the turn.