I have the 6260qc and the 6600mp. Since you said, you didn't want to have to upgrade for years, I would go with the 6600. It has the accufeed feature, and more. It was worth the price to me. I got an extension table with mine, and of course the attachment + accessories kit.
I love my machine.
If I had LOTS of money, I would have tried out a Bernina, a NICE one...to see if all they say about it, would be true for me, but, I spent as much as I could afford and quite happy anyway. :D
BTW, i still love my 6260qc, just wanted more bells and whistles, and to not be without a machine, when it came time for annual tuneup.