Depending on the encoder and settings used, the lowpass filter can be around 15.5 kHz with 128 kbps. Unless you're old or have hearing damage you should definitely be able to hear a difference in an ABX test.
Encoders also have changed a lot over the years and I can imagine that an old 128 kbps mp3 could sound very bad compared to a recently encoded one. Guess you're outta luck unless you have a lossless 'archive' or the original CDs.
Edited by xnor - 5/26/11 at 10:15am