The 3.2 is the most recent revision of the Mad Dog. Mr. Speakers makes changes/tweaks to the design of the Mad Dog and then incrementally changes the name of the can to reflect the current version. It's a nice touch so you can have some sort of basis when discussing and comparing different versions of the Mad Dog. The Mad Dog Pro is voiced/designed differently than the Mad Dog. Although they look similar they are supposed to sound different. I haven't heard the Mad Dog pro so I can't comment on them.
I think the Mids are where the Mad Dog shines. Voices sound relatively natural, full and very clear. When it comes to hip hop - instruments, samples, scratching, etc. all flow effortlessly with great separation and imaging. The bass isn't overwhelming nor in your face, but rather very defined and extends very well. Through my experience I've found the better source/amp in the chain the better the bass is defined. The bass impact can be adequate but sometimes lacks a bit. I've found it depends on the track though as lighter bass impact isn't necessarily a constant. I would not consider these bass head cans but I wouldn't classify them as bass light either. The treble is defined and relatively laid back. Overall these have a darker/warmer sound compared to a neutral headphone.
As for soundstage, it's not all that large but for a closed can I think it is very good. If soundstage is one of your main concerns, you might want to look into an open headphone.
Also, I noticed in your original post that you will be powering these out of your iPhone frequently. Although a mobile device can drive the Mad Dogs to reasonable levels of volume, these cans are planars and tend to like power. I can attest they perform better with an amp. I think the volume is suitable off a mobile device in a quiet area, but I took mine on a flight to see how they would perform in an airline environment and I found that my S3 simply couldn't provide them with enough juice.