Martin D ,I suspect you will not notice much of a bump in pic quality. But ,,the extra frames per sec could be helpful in some situations,,,and the massive amount of settings you can configure to your own personal needs will be a plus,,but can also be confusing at first to get things set up. You will also need reasonably fast Cards to take advantage of the high frame rate if you shoot at the highest Quality raw. If you use the flip out screen alot on your 77d,,you will miss that. Suspect but don't know you might gain some auto focus speed.
Yesterday,,people thought I was the best thing since sliced bread,,,,,to-day I am toast !