As I've explained hundreds of times over the years, a transformer has no impedance of it's own. Transformers simply reflect, bi-directionally, the impedance on one side to the other, multiplied by the square of the turns ratio - period. So, if you have a 600 Ω load on one side of a 1:1 transformer, the other winding will appear to have a 600 Ω impedance (plus the DC resistances of both windings). But, change that load to 2 kΩ and the other side will have approximately the same 2 kΩ impedance. That being said, transformer designs (number of turns, wire size, etc.) to perform best across the wide frequency range of audio by optimizing them for a certain range of impedances. Only in slang are transformers optimized for medium impedances referred to a "600 Ω" parts - and because that impedance was the standard for telephone lines and it trickled down into early tube gear and passive filters ... they are rarely used today.
The best transformer to achieve high noise rejection is a Faraday-shielded "input" transformer designed for high-impedance (10 kΩ or higher) circuits. Used at the receive end of a balanced line, they often have CMRR of 100 dB or more. It's difficult and expensive to make a Faraday-shielded "output" transformer (designed for low impedance) ... as illustrated by the Western Electric 111C or Jensen JT-11SSP series transformers. They offer high noise rejection and are suitable for 600 Ω sources and loads, but cost about 4 times what a good input transformer would to achieve the same high noise rejection.