There is a difference in the Dual Feed/IDT than a Walking Foot. The walking foot is mainly when you are quilting - the dual feed/IDT can be used at all times. Personally I have found a huge difference in my piecing with the this feature - although it is true you do not have to have it to piece. You may want to take some fabric and spend some time on both the Pfaffs and the Bernina new 7 series. If the Pfaff dealer is not close enough do you have a quilt show coming up in your area? A lot of times the machine dealers are there and you could combine that with your quilt show experience. In addition to the dual feed the new Berninas also have an expanded throat area and the bobbin holds probably about 70% more than other machines (with the exception of the Bernina 820/830 although it does hold more than even those). I am not a Bernina dealer but have been looking at the 710/750 seriously. I have a 730 and am considering selling it and upgrading.
I really feel that with buying any machine how comfortable you feel with it is what closes the deal. I do have an older pfaff which I purchased before Bernina came out with the new 7's however, I have found that if something goes wrong (which of course it did) parts for the older machines are really hard to get. It seems that most of the manufacturers have quit making parts for the older machines getting us to buy newer ones.