Yes, that is a descent deal on the new 686...
I have to agree with others... 4" will be more versatile so I would get that one first. If you still want the 6", get it later down the line..
I owned a 6" 686, first S&W I ever owned, bought it new in Nov of 2010 (for $719+tax). It was a great piece, accurate, attractive and I carried it in the woods frequently using either a sturdy belt holster or shoulder rig.
Not too long after I picked up a nice old model 19-3 with a 4"bbl. I found that when I was carrying for general purpose (not hunting) I took the 19 out of the safe and left the 686 most times. Point being, once you carry a 4" wheelgun a bit, the 6" will lose some appeal, at least for general purpose carry..
I did end up trading the 686 in on something I wanted more. It was/is still a bittersweet choice. I miss it.... I currently do not own an L-frame, but plan to get another 686 in the future... I may even go with the 6" again as I have my m19 for carry. IDK, I'll make that decision when the time comes... My brother has a 4" that I have fired more than a few times and I really like it, so I could just as easily go that route too...
My advice: If you narrow it down to a 686 over other brands/models, get the 4".