I'll chime in on this since I went from a zhp to an m3..
As for the zhp and the m3, it depends they were both amazing cars, reason I went to an m3 was not because I didn't like the zhp, in fact the zhp was an awesome car and I owned it for 6 years. I moved to the m3 because I got kinda bored with the power the zhp lacked, and I have always wanted an m3. I would have purchased an m3 back in 2006 when I purchased but the m3 was slightly out of my budget at the time..
Some one said that the zhp brakes were better than an m3? I call bs on that one. As for the handling, it is very similar but I still think the m3 has a tighter feel to it.
I had originally posted my zhp for sale last year and had a few people look at it and the typical tire kickers, but no bites. So I decided to keep the car until a friend of mine brother was interested in a zhp and wanted to see what the alcantara looked and felt like, and absolutely fell in love with it and pretty much put me on the spot to buy it off of me at my willing to sell price.. I looked saw an m3 that fit my standards and made the decision to move on.. I'm happy with my decision
If you go from the m3 to a zhp you will be happy but you may get bored of the zhp power if your used to the m3 power