Yes, I love my 6600, too. I've FMQ'd so many quilts with it, I've lost count. It's a great machine, and I usually FMQ and piece with it at full speed, but have noticed lately that I need to slow down my hand speed during FMQ in order to keep my stitches the right size, and have been thinking about purchasing a faster machine for piecing.
I just think it's strange that it goes so much faster with the foot pedal, my dealer didn't think there should be any difference, but couldn't find anything wrong with the switch... If anyone who currently owns a 6600 would give test the speed with the foot pedal vs the start/stop button, I would really appreciate it.
I really should take the time to learn to upload photos of some of my quilts... I'm just too lazy, and it never seems very intuitive to me... I lose interest in figuring it out.