According to the Bellanca Owner's Manual that I have for the very early Citabrias, the 7GCBC was available with either the Lycoming O-235-C1 (115 HP), or the O-320-A2B (150 HP). I strongly suspect that the vast majority went out the door with the 150 HP engine... The only significant difference between the 7ECA (115 HP) and the 7GCBC (115 HP) were the "flapped wings" on the 7GCBC, which gave it a lower stall speed and reduced takeoff / landing distances. The book says that the O-235 version was about 73 lbs lighter, climbed a little slower (728 fpm v.s. 1145 fpm), and that sea-level takeoff over a 50' obstacle were somewhat longer as well (860 ft v.s. 525 ft). Those performance numbers seem a bit "optimistic" to me.
As for relative performance versus the Champ... As I understand it, the changes to the structure to allow aerobatic certification of the Citabrias raised the empty weight over the Champ fairly substantially, and as someone else mentioned, weight has a big impact on takeoff / climb performance. A look at empty weights of the current ACA Champ and 7ECA shows the 7ECA @ 1120 lbs empty, and the 7EC @ 925 lbs empty. That's almost 200 lbs difference, with both aircraft similarly equipped. The difference was probably a bit bigger with the original wood spars, and when Champs had no electrical systems, and were powered by smaller, lighter engines. Cubs and Champs are great illustrations of the "simplify and add lightness" performance formula!