I have a Dolby 422 unit and a Dolby 330 but the 330 hasn't arrived yet so I haven't done a direct comparison on the two units.
The thing with the Dolby 422 unit is that it was made for cassette and VHS tape duplication and it shipped with various filters installed depending on the application. Roger Ginsley of Tekx Electronics did some bench testing of the unit for me a few weeks ago and created some print-outs of the frequency response with and without the cards installed. The cassette filter rolls off the high frequency response at 16,000 and the VHS has a notch filter for video. By pulling the filter cards you get a flat frequency response out to 22,000 and then it rolls off to 25,000.
The 422 is also a more complex unit and offers Dolby B, C and an optional S - not SR but a "new and improved" consumer format which was intended to replace Dolby B and C for cassettes.
Once I get a chance to use both I'll post what I hear.
Rick