I haven't heard of Cardinal Tetras nipping at Angelfish's fins. I really doubt they will. In fact, I think they're perfect tankmates
If you get 4 Angelfish and 1 Pleco that grows to be 5 - 8", then you can certainly have a beautiful school of Cardinal Tetras either in a 55 gallon or in a 75 gallon tank.
4 Angelfish = approx. 20"
1 Pleco = approx. 8"
TOTAL = 28"
In a 55 gallon tank, that leaves you with additional 27" of free space for Cardinal Tetras. You could have as many as 13 Cardinal Tetras in a 55 gallon tank. But, as always, subtract some inches for gravel and decor (they take up a few gallons of water too). So, say about 10 Cardinal Tetras?
In a 75 gallon tank, that leaves you with 47" of space left ... which means you could have as many as 23 Cardinal Tetras

... but make it 20 maybe.
P.S. I still think 4 Angelfish in a 55 gallon tank are too many. It's not because of space but because of Angelfish's temperaments.
If you're getting a larger tank anyway, why not get the 75 gallon one? It will be much much better for 4 Angelfish, believe me.