A month ago I did a comparison between both pianos to disoblidge a friend. He has had to made the same decision like you. He send me a MIDI file and a wav-file of the same piece with the Ivory-piano, so I made for him the same piece played with the Vienna Imperial. To say it clear:
It's not really possible to make a real comparison for somebody. For myself I can say: In this comparison I realized the quality of the vienna imperial. The Vienna Imperial is simple in a different league. With using the low velocitys you can achieve a v e r y warm, dark and deep sound, the analyser I've used shows clear what happens in the depth range; a sound which is necessary for a very close and warm sound, how it is mostly used in pop-solo-piano music; you will not find this kind of depth in the Ivory piano.
A lot of other differents are to ascertain (numbers of velocity layers, possibilities of Dynamic and MIDI Dynamic range setting (very important for real-time playing) . The most important thing for me is: With the vienna imperial you have a wide range of choice for achieving the sound you aiming for. The Ivory sounds good, but the possibilities of sound processing are much less.
So if you work only in one style or kind of music and the sound of the Ivory fits, this piano is a good choice. For more flexibilty you will really enjoy the vienna imperial.
Kind regards
Frank