I have the 6600 and my other machine was 15yrs+ old. I cannot tell you the difference it has made. The accu-feed is absolutely wonderful. I love that the walking foot is attached, it has a thread cutter, knee lifter, etc.
When I went out shopping for a new machine I took DH with me. He's a Mech. Eng. so I had him ask all the questions to how the machine was built. The Janome is the only one we came across that was ball-bearing!!! It'll last a life time. A lot of others out there have plastic insides. Be careful!!! Don't just look at the bells and whistles, take a closer look for your own benefit and your pocketbooks.