I recently bought the CB 3500 from Bob. I'm quite the stitching machine novice myself, but we're getting along very well, and I gain more comfort and confidence with it every day.
I remember the 4500 sitting next to it, and passed on it because I didn't think I could get it in my car.......seriously, I just don't need an arm that long.....the 3500 fits me just fine.
From what I understand, the CB 4500 and the Cobra Class 4 are basically the same machine, but again, I'm a novice, so what do I know?
Good luck.......hook em Horns!!