I don't know the 6500, but I have had my 6600 for four years, and I love it. Never eats the beginning of a block (no need for leaders), sews through anything (3/4 layers of denim), cuts thread beautifully, and on and on. I love the walking foot - always feeds well with no puckers. No repairs, just routine cleaning. I can't imagine a better machine for the $1500 I paid for her.