I have 09 Ions and I like them. I have usually rode stiffer non-Burton boots, so these felt 'softer' than what I was used to, but still very very supportive. Havent rode or tried the Driver X, but heres my take on my Ions. Im 6'0, 190.
1. The did get softer, have about 40 days on them, after a couple days, but I normally give boots a good break in before I even take them out to the snow. Got softer, but never felt that they got mush. Still supportive, still comfy.
2. Not sure.
3. The heel pad is worthless imo. Didnt feel any diff. The only thing I notice is the pocket makes the sole super soft in that area and it gets really wet. Im afraid that if I didnt take the airbag out everyday, some mold will surely grow in there.
4. Its all preference.
All in all, the Ion was/is a good boot. I wish it had an articulating cuff, and the toebox feel a little small compared to some other models. I also noticed they get a lot colder(due to shrinkage?) than other boots Ive had. I liked it, but upgraded to the SLX this year.