Hi....I upgraded to this machine last year. I bought it second hand.
I have been really delighted with it...it is a dream ..but it did take a little getting used to. I love the flat bed and the table extension, they both make life so much easier and I don't miss having a free arm at all.
The quality of stitch is excellent and so many to choose from.
Free hand quilting was abit problematic to begin with but someone gave me the great idea to keep the feed dogs up and now it is lovely.
Would I buy it again...absolutely....don't know what the 7700 is like but that was out of my price range anyway.
Only tiny issue is the paint does chip...so handle it with care...
I have a smaller Janome for classes and previously had a Pfaff Select 3 and have a Husqvarna Designer 1 which I use mainly for embroidery but the 6600 is most definatly my favourite!