Hey everyone,
Thank you all so very much for your comments. Sorry I'm late with this reply, things in Vancouver are so busy right now it's hard to keep track of things right now.
I really appreciate the insight into these great machines. I am going to go with the 664 and get to work most likely by the end of the year I'll end up with a 688, that sl-6 combo is quite enticing, but for now the 664 wins out.
Cheers!