I've posted about this a few times. For piano technique, they don't really compare, the 88 feels much more piano-like. The 73, having the lighter action, is arguably better for rhodes, wurly, and clav.
I think it's more appropriate to compare the CP73 to keyboards that similarly sacrifice action for portability, and in that category it's the best action I've found. I also far prefer it over Korg's RH3. However, I haven't played the newest Casio weighted action, which some people rave about, so can't compare it to that.
How do you like your cp73 compared to your seven ? I know some of the sevens sounds from my gemini and I know the older yamaha cp5 . Thank you