I have both. I've had their cages next to each other before, but Matilda isn't very friendly with other birds. She's very clever though... she used to call "Lilllllllllly" and "Pop-pop-Poppy" hoping they would get close enough to bite at. Of course they were never close enough to reach, but they did fall for her charm and go near.
That's not to say yours won't be 100% friendlier, but I've heard of a CAG totally biting off a conures beak before. So it's not something I'm prepared to try personally. I've found CAGs to be great birds, but very temperamental and pretty much the opposite to my easy going sun.
A lot of birds that are friends have little spats, but with the size difference it could end up tragic. However, I've seen a B&G sitting quite happy with a sun... just to contradict myself and my concerns there
