I have the QE 4.0. The QE 4.2 was released a couple of months ago, so there should be some good deals just now. All of the Expression line have IDT, so no need for a walking foot.
One feature the 4 has, the others don't, is auto-pivot. This automatically raises the presser foot a little in the needle down position when you top sewing. Brilliant for machine appliqué!